SMZ-TMP DS and stomach

I broke out in a slightly raised rash that started on my chest and spread to my arms, stomach and legs. I thought I had fifths disease except that there was no fever or runny nose before the rash appeared. According to the pharmacy - you can have a severe reaction to it if you are allergic to sulfa drugs (which I am). Next time I won't be so quick to believe everything my doctor says before trying something new..

I was prescribed SMZ/TMP DS 800-160 for a UTI...one pill twice a day. I had been taking it for 2 days. On the 3rd day, I broke out in hives in areas on my chest, sides, back and stomach and the next day started noticing small bumps on my arms and legs, too, that weren't as small and irritating as the hives the day before. Needless to say, I stopped taking it that day, the 4th day. However, it's the 3rd day since I've stopped taking it and I am still itching and skin is still broken out. This medicine had also caused a loss of appetite and altered my taste buds, but the break out is the worst of all and is ongoing, unlike the other side effects which were back to normal shortly after I stopped taking the pills. If anyone else has experienced the skin irritations, how long did it take for it to stop after taking the pills?

I was prescribed /TWP DS 800-160 for a urinary infection. I have taken this medication before with no ill effects, but this time my hands itch all the time and I have a red, itchy rash on my back and stomach. I finished the prescription today, ao hope it goes away and so far the UTI I had is better. At least I don't have as much pain, but it required two prescriptions before is worked. I have taken this before with no noticeable effects. Is this serious?