What Causes Itchy Pimples On Palms And Hands?

three weeks ago i had what i thought was a spider bite mid thigh. then i began breaking out in pimple like places. they itch terribly, ooze a lil, produce heat and get sore. mostly on my left knee with one on my shin and one near my ankle. a few coming up on my right knee. i am a ra patient. i did go to my np yesterday. she gave me a shot of solumedrol and told me to use hydrocortisone cream as she felt it is bug bites. no one else in my household is experiencing anything similar. i take prednisone everyday. could it be a joint infection? this morning my right knee itched incredibly bad along with the palms of my hands. the roids did nothing.