Weird things going on with my body, any help would be appreciated?

Lately I have been finding odd, hard abd painful pimple like spots on my body. They usually appear one at a time, and will eventually blister, break open and scab, turning red all around the area, and then a hole is left in the center. It seems to me like little spider bites almost, but it seems so very random and unlikely. I have around 5 right now. But as if that's not enough, a few days ago I woke up with a huge, swollen bruise on my knee with 6 "pinprick" like holes in a line around the bruise. Its super swollen, and I tried to see what would happen if I squeezed the pricks and fluid came out a bit. It's freaking me out enormously. Please help, any advice would be wonderful.