I agree with kaliope that professional help is necessary if you want to find stability. Therapy and medication has helped me immensely.

I am 21 and notice several similarities between your situation and mine - or, rather, my situation a few years ago. I, too, tried vitamins to control my moods, and ultimately they were not effective when I encountered deep depression, anxiety, or hypomania. You mention that you experienced unpleasant side effects from your medication. My psychiatrist (who has labeled me as "bipolar-ish" ) has me on a cocktail of medications that took me years to fine-tune, but at this point I suffer no side effects and feel stable. I'm not on typical bipolar medications, but his view is that as long as I'm stable it doesn't matter what he calls me or whether I'm taking typical medication for one diagnosis or another.

The tendency to switch from one thing to another is something I have as well. When I want to quit something, I think about it this way (and believe me, I still do quit things sometimes...constant battle): many people change locations to escape something. They believe that starting at a new location will be a "fresh start", and essentially their previous problems will be gone. From personal experience, I can say this is not the case. I could be wrong, but from your post it sounds like your difficulty stems not from the individual jobs, but from the general commitment of having a job itself. And once someone experiences that difficulty, it's so enticing to leave the job and find a new one for that "fresh start" (TRUST me, if you are in fact feeling this way I understand!). In the long run, though, I've found that stability and sticking with something, even when completing a task or going to work is downright painful, that I ultimately feel a great sense of reward for my commitment when I do follow through with my tasks.

Here are a few other things that have helped me find stability in the past few years:
- Exercise. My almost-daily yoga practice (at home) keeps me STABLE! Find something you love and it won't be hard to stick with it, but keep in mind forming a habit or routine may take time.
-Eating well. Personally I am vegan, but my overall diet is one that generally avoids a lot of sugar, processed foods, etc. But I know this is hard at college sometimes...
-Taking control of my schedule. Why are you experiencing such work-related stress and anxiety? Is it your hours, your type of job, your boss, your coworkers? If your job is really miserable, look for one that is different (waitress vs. retail, for example). Ultimately, jobs suck and people suck at this age, but they're necessary

Sending hugs your way.