Staph infection or spider bite? help?!?

This is how it went. I previously asked a question about my spider bites.. I went to the doctor yesterday and they told me it looked like Staph. So, they put me on antibiotics which I'm taking now. This is my second day taking them. My question is, Was I actually being bitten more than once on my butt (recently had 4 sores in one area.) or did the staph or mrsa spread and cause my most recent sore? and on a side note I had been getting these very infected sores in my armpits. I thought it was from deodorant so i changed what i used, it helped a little but then they came back. i usually would get a series of three or more. one after the other would come. each after the other would drain and start to heal(my last flare up with that was in august of 2010). Could i have had MRSA in my bloodstream and just not have realized it or the Staph and it flared up from the original spider bite n my butt? I might want to add that my immune system isnt the best. the new bite the doctor told me looks like Staph but is it just spread from the other sores? or could it be a new actual bite? it has two tiny holes I can see. and very infected. please help?! am i going to die from this?