What Causes Bumps On Arms And Shoulders?

I have red raised bumps on my lower arm, only two, and now two or three similar bumps on each side of my neck/shoulder. They're not itchy but are hurtful and uncomfortable. The dermatologist and friends think it looks like bites. But I don't remember getting bit and don't spend time outside, except on May 30 I do feel I got bit by a mosquito on my left underarm right below my wrist which always was flat and small. At the same time a little later noticed the red bump on the same arm (lower). They lasted about 4-5 days; then came the left arm marks. Any clue to what these marks are from?