Large raw painful sore on back of thigh keeps growing and is not healing

[72777]

I am 30 years old, and 20 weeks pregnant with my third child. About 5 weeks ago I noticed a small pimple like sore on the back of my thigh. It looked almost identical to a pimple ( without the white head ). Gradually the sore got larger and more painful. At 2 weeks I went to a walk-in clinic, where I was perscribed fucidin cream and amoxicillin tablets. No improvement, sore increased in size and infection spread causing redness and swelling over a 6-8" diameter. A week later, I went back to the walk-in clinic and had the doctor try to lance the sore and squeeze it out. Nothing came out of the wound. A week later, at the 4th week I saw my family doctor who perscribed cephalexin tablets for 7 days, which also did not help. I attempted to push through and hope it would clear up on its own, however it progressively got worse still, to the point where I went to the hospital to seek another opinion. The hospital tried lancing the sore at that time and again no puss was expelled. Following that, the same doctor did an ultrasound on the sore to determine whether there was any puss below the surface or in the muscles. The ultrasound showed there was nothing much in the sore. He then perscribed clindamycin for 10 days. Halfway through this perscription I had a negative reaction and had to stop taking them. I am at my wits end, and teetering on depression. Please help!!To describe the sore, it is a raw ring ( like a freshly pealed scab, about 1.5-1.75" in diameter, with a 1" hard white/black scab in the middle.

[KimmiScott]

It looks like a spider bite.