Wow, Im exhausted just reading that! Actually, I know exactly how you feel since I went through all those emotions in my early 20's; you feel lost and unsure and confused. I'll try and give you some advice from my experience without going all Dr Phil on you.
I was an admin assistant for about 5 years and I did enjoy it although it got to the point for me where I wasnt able to be challenged anymore and like you, I wondered what I was doing to make the world a better place just by answering phones and pushing paper around. Im still in admin now and although I get a lot more mental stimulation, I still dont feel like my job is worthwhile to humankind, even though I know it is to the company. I am not qualified to be a nurse or a doctor or a lawyer or a teacher and dont really want to do any of those things anyway, so I look at what I can do outside of work. So, I volunteer at a dogs refuge where I take my puppies out for walks every week. I know I cant contribute anything finanically, and I can only give about 4 hours of my week to them, but I imagine what those 4 hours mean to to the dogs in my group. For that short amount of time every week, they get out of their kennels and can behave like dogs are supposed to and all their worries go away. And the looks on their faces make it all worthwhile. My point is, you dont necessarily need to save the world in your job, and you dont need to do something on a huge scale to change someones life. I dont have any career ambition either, except to have a laugh in my job, work hard and keep learning, and thats enough for me.
If your managers are being asses, say something. Write down what you expect from your job, how you want to be treated and demand it. If they dont like it, find another job. You obviously are an intelligent woman and I really believe that for most people, the days where the employer can push you around and feel like they are 'doing you a favour' by employing you are gone. You are as valuable to them as they are to you; it should a partnership where both you and your employer get what you want and together you work hard to make the company successful.
So, you know you dont eat healthy and you dont exercise. Is there any medical reason why you cant exercise or eat certain foods? If not, change it. Write up a menu plan and stick it on your fridge. Take fruit and vegetables to work to eat while you are at your desk. You should be exercsing your puppy, so go for a walk after work with her in a park; throw a ball, run with her. Thats exercise. It is so easy to get in a rut, but if you can give yourself a kick it is even easier to get out of.
Do you love your puppy? Are you glad you got her? Does she bring something to your life that was missing? Sorry if this sounds harsh, but if so, tough luck that your boyfriend doesnt approve. Your dog is not a 5-10 year financial burden to you; she is a friend and I would think worth every cent you spend on her. And a dog will NEVER disappoint you.
I think you need to slow down a bit and to look at things in a different way. Realise that this is life; and yes, crap happens. Every day, in fact. But it doesn't have to make us pessimistic about the world. There will always be good people and bad people and terrible things will happen. But its all a part of our journey here. I have had some horrible experiences, and of course if I had my way I would never want them to happen again, but I found the lesson in them, and once you can do that, you can at least understand why it happens. My turning point came when I was 25, when I woke up and realised that the reason I was confused was because I hadnt done all the things that I was 'supposed' to do that age. I didnt have a degree, money in the bank, a share portfolio, a husband, the white picket fence with my 2.3 kids. And I realised that I didnt actually want all that. My life is about me, not what others think it should be. Now Im approaching the big 3-0, my thinking has totally turned around. I still dont have any of those things, but I love that I am single and have no responsibilities, I love that I am able to earn enough money to live on my own and support myself, I love that I am a strong and intelligent woman, I love that I have beautiful friends and the best family in the world, and I love that I finally love who I am. It took a lot of hard work to get here but it was all worth it, and I really hope that you get here too because it is the best feeling in the world.
You dont 'have' to know where your life is going in order to live it; it could be over tomorrow or you could live for another 70 years. Take some baby steps in order to get things on track; deal with one thing at a time and work out what you want for today. I would really start by getting your eating and exercising sorted out, it makes your head clearer.
Sorry about the length of this; and this was the edited version! I wish you all the best and if you need any more advice, I will give you all that I can.