Insect bite or skin condition?

Last week when I woke up I had about three itchy red bumps on my rear end near the right hip, a couple near the left hip, and one on my back near my armpit. I haven't been bitten since then. What kind of bug could bite me there when I'm wearing sweat pants and underwear? I would suspect bedbugs but it happened only one night. Could I have been bitten before bed and only noticed it the next day? Could it be a skin condition? It seems more like an insect bite.