Antibiotic mix?

I recently had a very bad and itchy boil/carbuncle. I've had some big ones in the past but nothing too serious because after all they resolved on their own naturally.
This time however, it was accompanied by a low grade fever so I knew this was something next level.
Went to the doctor, she prescribed me an antibiotic mix of cephalexin and clindamycin.
When my boil came to a head and was drained, a culture was taken and I was given an IV drip of (I think) the cephalexin. They also ran a lab on the culture. It was found to be a result of staph.
So the doctor took me off both meds and prescribed Bactrim.
A day after taking the Bactrim, I noticed a rash beginning to develop. The rash quickly spread and at first it wasn't itchy but that changed.
I told the doctor about it and she changed my prescription to yet another antibiotic, Doxycycline.
Here's my question, the rash has spread all over my body and taking antihistamine (Banophen) doesn't really help, it only makes me sleepy.
Has anyone had any similar experience as mine?
Im afraid to take ANY antibiotics and am only taking the antihistamine. I'm just plain scared to do anything at this point and am going to see the doctor tomorrow again to figure out what is my next step.