So, I contracted a staph infection from a hot tub on vacation. Was placed on Bactrim (which I have had in the past, with no problems....) I took 2 pills a day for 10 days, & THEN broke out in head-to-toe HIVES. Terrible, itchy, HOT to the touch hives. My doctor told me to go off the meds (which I had already finished.) Now, 4 days after my last pill, I have the worst anxiety I can possibly imagine having. My body will start shaking, where I cannot hold still. I will get awful stomach pains and feel dizzy. Then I'll start to feel better. A little time will go by, and I'll be dizzy, very ill-feeling, and either burning up or freezing cold. Most of the bumps are completely gone, but I feel more sick than ever.
What are the risidual effects of Bactrim build-up internally?
I have NEVER experienced anxiety before, but this is unbearable. I don't want to leave the house, and when I drive, I feel dizzy and out-of-control. I feel like a stranger to my own body.
What is going on??

You need to go back to the doctor. Some allergies can go on for 2 weeks from drugs. In fact you might consult an allergist for better treatments.

Antihistamines and some other medications might be in order.

Bactrim is a long acting sulfonamide...it remains in your system for a while. Avoid all sun exposure for the next two weeks and NO TANNING beds either.