Current source symptoms and conditions

Was prescribed Sulfamethoxazole-Trimethoprim 3 days ago for a bacterial skin infection. At the same time, I also had an apparent allergic reaction going on (unknown source, had never had one before) where my arms were both covered with hives/welts. So my skin was peeling and hive covered BEFORE even starting the meds, which is making the evaluating of the drug side effects a bit trickier. So far, the skin seems to be improving but the hives/rash has not improved, despite taking prescribed allergy meds during the same time. So this could be the current source of the rash, but I can't tell.
On the plus side, have not had any stomach upset (I took all doses w/ food) or other GI symptoms other than increased frequency in BMs. I only seemed to get a headache after not drinking water for a couple of hours. If online sources are to be believed, the "sulfa" portion of this is the culprit behind the worst side effects, AND food may interfere with absorption/effectiveness. Based on that, I'm planning on taking my remaining doses w/ food since the skin infection is already clearing up after 2 days and I've got 10 days to go. Hoping to avoid the reactions folks described here where they starting rashes late in the treatment cycle.