Red bumps on my upper back?

So I randomly noticed yesterday that I had a patch of bumps on my back yesterday, and I initially thought that they might be acne because I'm at that age where acne is a common occurrence. However, today I felt they have spread across my upper back, and my mom looked and told me it wasn't acne, but a bunch of red bumps. What could this potentially be? I haven't been exposed to anything unfamiliar, and I wash my back on a regular basis, so I have no idea what it could potentially be.