I have itchy, red, zits on only one leg, that become bruises. Three friends have them too. what are they?!?

I took anti-biotics for them a two weeks ago and they stopped. Two weeks after I was done with the pills, they came back. They look alot like foliculitis, but my friend gets them on his arms (he doesn't shave there). They're really itchy like mosquito bites, but they look like acne, and they seem to be in the hair follicle. Sometimes they cause a big bruise. They cause purple scars as well. And they're not in clumps. They're spread out on my right leg. (mostly on the calf) I've tried using a different razor, wearing insect repellant to bed, washing my sheets, sleeping somewhere else, wearing long pajamas, rubbing my leg with alcohol, hydrocortizone... nothing gets rid of them! What can they be?