Becky. I am so so sorry. I did not see your posting until now. I think you have made a very wise decision being honest with your boss and then asking for some time off. I have had so many thoughts after reading your post so I'm just going to respond to them in the unorganized order that they are coming out of my head.
First, I have found from experience that even though you spend more time with your co-workers than you probably do with your own family, they are not to be trusted like your family or a true friend outside of work. My therapist once described co-worker friends to me as "situational" friends. As long as a situation is good they are good. However, when a situation changes and has some effect on them, they will change to reflect that situation. For the most part, people from work are unfortunately usually interested in themselves first and foremost. Second, if they are being mean or avoiding you with another co-worker, realize that they would turn against that co-worker in a second too, if it was to their own advantage.
Second, I know it is hard to be in an environment where you are the victim of this. But right now you have other much more important things to deal with....so pack this issue aside in another suitcase to deal with later.
Third, I think time off is a wonderful idea. From a bosses viewpoint, you are not being irresponsible by calling in sick over and over again. You are assuming responsibility by admitting you have a health problem and you want to take care of it and get yourself better again so you can go back to work. Moreover, if you are taking vacation time for this (and I'm not sure if you are) that shows more initiative that you are not just trying to take advantage of the system like so many others do.
Fourth, with this time off you can take yourself out of the fire, so to speak, and concentrate on the most important thing: YOUR HEALTH! Go get whatever tests you need, make any and all doctors appointments that you need. Nip this in the bud so that you can finally feel better. And by taking this time you will be bringing your stress level down. And that alone, will bring some relief to your symptoms.
Last, as to why people can be and are so mean? That's a fair and sad question. My guess is they have either bitterness, unhappiness or boredom in their own lives and unfortunately do not have anything better to do. They are bullies who have never learned how to grow up. And if they have children, I feel bad for those kids because look what "values" their parents are probably instilling in them........
Just take this valuable time and spend it taking care of yourself both physically and emotionally. And if you need some help post again (I promise to look regularly) and I'll be here.