What would cause this to happen?

I have been in college for two years now ( part time ) and I got a cosmetology license right out of high school. I lost interest in cosmetology while in college to persue a career that I feel pionate about, and recently, I took a CNA course because I thought it might be a rewarding job while I continue to stay in school, and I ped my boards, got my license, and now I have lost interest; furthermore, my fiancee helped pay for the course, and I am currently unemployed because I quit the shop I was working at, but yet I feel so unmotivated to do anything, even though I want to contribute something. I have a medical condition. I suffer from hypothyroid, and I also have bad anxiety these days. I see a doctor every month right now and he keeps changing my scripts plus does bloodwork frequently. I have been feeling really down and hopeless lately, and I'm always tired. My physical symptoms are frequent dizziness and heart palps, sometimes an irregular heartbeat. As far as the lack of motivation goes, that's not like the old me at all. What would cause this to happen? :(