I Am On A Round Of Antibiotics. This Is My

I am on a round of antibiotics. This is my second round. The first round was cephalexin 500mg took 3 times a day for 10 days for what was thought to be a spider bite. My dr lanced and drained the "bite" and put me on the antibiotics. Then a week later I had another lump show up looking like a spider bite, this time he didn't lance it and put me on sulfameth/trimethoprim 800/160mg tb. My questions are how do I know if the antibiotic is working? I'm pretty sure I have a staph infection, how do I know if it's MRSA or just another staph infection? What signs do I need to look out for if I need to rush to er? I'm an over thinker with high anxiety and I'm freaking out over every little feeling. I don't want TSS, I don't know if my body is reacting to the antibiotics, I don't want to die.