My Husband Was Diagnosed With Second Degree Burns On Inner

My husband was diagnosed with second degree burns on inner top leg from boiling water and was given bactrim ds 800 generic SMz tmp ds 800 160 tabs on 1 10 2017 and he has been nausea weak headache and feels horrible but was ok with this med for 2 days and now he just feelin worse no insurance went to urgent care and seen by nurse practitioner and given sulfa cream and taken ibuprofen for headache and did not taken his dose tonight because of e severe headache wound was cleaned and changed by nurse for wound care and I changed them yesterday burn larger than 3 inches the nurse said it looked better Should he be given a new med or continue on this drug