driving myself insane

I need help :( every since I had "relations" with my guy friend in September, my life took a terrible turn. My stress went through the roof (Bc I thought I could be pregnant and I'm not), school was starting, and I felt like an idiot for doing what I did with that friend. Every since then I've been having all these horrible symptoms (dizziness, stomach problems, fatigue, shaking,...) and I don't know if there's something actually wrong with me or if it's my anxiety. I am not the person I was before that night, and I'm missing my old self so much. I'm just so sad and terrified and anxious ALL the TIME, and it's literally driving me insane. I used to be a happy go lucky, sociable, fun person and now I'm just scared, hurt, constantly thinking about what is wrong with me, etc... I've been to the regular doctor and she just said my vitamin d was low and I might have GERD, so she gave me these pills for it but I don't want to take them (not a pill person). So just idk, if anyone has good coping mechanisms for severe stress please let me know!