You and I share similar problems. I'm 27, and I've been through a lot of what you described. Also, I was raised a Baptist, and I'm a Christian as well. When I was 17, I began questioning my faith and rebelling against it privately. Unfortunately, I was deeply involved with several ministries at my church, and it made it impossible to stop going to church altogether. If I hadn't been involved in those ministries, then I would have given up church completely. Now, I've cut back on some of my involvement, and I avoid going to services, etc. Frankly, I've strayed from my faith and I'm not sure how to get it back. It's been to the point where I even question the existence of God. It seems that the only time I do pray is when I'm attacked by anxiety, or if I'm facing a very serious situation. Therefore, I must still believe in God. However, there have been times where I prayed for peace during a bout of anxiety, and it didn't work. So, in the process of dealing with all of my other stuff, I've been dealing with hard spiritual issues as well. It's good that you pray - I've read that people who do pray often are able to cope better with pain and hardship.
I've had depression for about 10 years as well. It's terrible. It ruined my life. Because of depression and anxiety, I screwed up college. Even though I've gone back to finish my degree, it's taken me 10 years and a butchered transcript to do it. My finances couldn't be worse for a person my age. There is no way for me to support myself financially, and I've likely ruined any chance to rent or buy a place to live, or to get a loan for a car, etc. My parents are still supporting me, though I do work part-time and pay for some of my stuff. Anxiety attacks would come without warning, and general anxiety affected my ability to function on a daily basis. Thus, the most basic parts of life became a huge job. I withdrew from people, family, friends, lost interest in everything, had no inspiration to continue life, and felt that I would end up alone.
Worst of all, I was (and still consider myself to be) a hypochondriac. Like you, I constantly worried about my health. Cancer was always at the forefront of my thoughts. If I didn't have some kind of health problem going on, I felt abnormal. I was always feeling symptoms of something and would spend hours on the internet researching it. Of course, this only made it worse. Family would roll their eyes every time I described a new pain. I was always convinced that I had something life-threatening and that I'd end up in the hospital sooner or later. No one may believe me, but they'd be sorry when they found out that it was a legitimate illness. I have some relatives who have dealt with cancer, and my father has colon polyps that he has screened regularly so that they don't develop into cancer. I've even had some intestinal symptoms that could be associated with some sort of disease, but I've found that stress was causing the majority of my symptoms. The more stress you put yourself under by worrying about things, the more physical symptoms you will feel, and that only leads to more intense worrying. It's a cycle that you have to make the decision to stop.
I've had a benign tumor in my breast before and I was scared that it would be breast cancer. There have been a couple of times where I've had unusual pains and I got worked up over what turned out to nothing. The reality of your colon worries are that your symptoms could be something else other than cancer. In fact, they could be due to stress and anxiety. Polyps can have some of the same symptoms, but they're not dangerous unless you allow them to develop into tumors. That's why my dad checks his so that they can catch anything before it turns cancerous. So, I would do the colonoscopy because the likelihood that it is cancer is slim. If they catch it early enough, it's not life-threatening. Once you do it, then you'll feel a tremendous weight lifted from your shoulders. Even though you don't want to know if it's bad news, you've got to have the courage to face it. I think that just KNOWING either way will be better than putting yourself through torture of not knowing. And keep in mind that it's more likely that the news will be good.
I have the same problem with breast exams. I'm so squeamish that I don't like touching myself that way. I don't even like taking my pulse. So, I've gone for more than a year without a self-exam. That's not smart on my part because of my past fibroid tumor. But I also don't have a history of breast cancer in my family - that doesn't mean that I can't get it.
Like you, I put on an act in front of other people. No one other than my family knew what a mess I really was. I still put on an act because I haven't resolved some of my issues. What I have learned, though, is that worrying about being sick just makes things worse. I've found that if I dismiss it and stop being so sensitive to every sensation in my body, I can function much more normally. Now, I've gotten rid of a lot of anxiety. So, have courage.
Here's what I would do in your situation:
1) Get a colonoscopy. I promise that it will make you feel better, and relieve your mind. Chances are that you don't have cancer, and you've built up the whole situation in your mind. Once you know that you don't have it, can you imagine how much better you'll feel? You've got to stop thinking so negatively about everything and start thinking positively. Go into the doctor's office like nothing is wrong, it's just a preventative measure. Think of it this way: what would your life be like if you were perfectly healthy and had no life-threatening illnesses to worry about? Wouldn't that be great? What if that is already true, but you've convinced yourself that it's not? What if it's all in your mind? Now start thinking positively for a change, get checked out, and stop worrying about it.
2) Find some ways to get involved with other people. Do something with your church. Go to someplace with friends. Find some hobbies that you can get involved with. Decided you want to do something and just go for it. Change your whole way of thinking, and then act upon it.
3) Start exercising. At the beginning of the year when I was having debilitating anxiety attacks, I started exercising daily. This built up my self esteem and many of my fears vanished. Sounds simple, but it works.
We can talk more - let me know how you feel about what I said.