For The Last Couple Months I Have Been Getting Red

For the last couple months I have been getting red bumps on my skin. They look like insect bites or pimples, but they do not hurt or itch. They fade in a few days, but there are always new ones too. It used to be just a few random ones at a time, but occassionally I'll get 15-20 in the same region (typically around my mid-section, hips, upper thighs). I also get them on my arms and even my hands occasionally. I haven't changed anything external (lotions, detergent, soaps, etc), so I'm not sure what is causing this. Any ideas? I haven't been too concerned since they don't bother me, but I don't want to just ignore if it's a symptom of something else going on. Thanks!