bacterial skin infection
"I'm on my fourth 800/160 pill of bactrim treating MRSA infection which has also caused my lymph nodes behind knee and groin to swell and  hurt.  I initially took doxycycline for about 4 days with worsening infection.  Bactrim worked day 1.   The infection started to clear and lymph swelling and pain is going away. 
Unfortunately I had severe anxiety including shaking tightness in chest very dizzy and feelings of doom.  It's possible this was brought on by me overreacting to a slight side effect but this is a very strong antibiotic. It works but you might have to suffer through it.  Not fun"