Cluster of large bumps on upper arms

[phe001]

Around 7-8 weeks ago I simultaneously developed two different-but-similar types of odd bumps on the back of each of my upper arms that I haven't experienced before, and haven't gone away since.

The first is a cluster of about 10-20 colorless bumps. They're within a one-inch diameter area, and each one is fairly large as far as skin stuff goes -- about 2mm across -- which seems to rule out keratosis pilaris (which I've had before, so I can easily recognize). They don't itch/hurt, and haven't changed in size, color, or anything. Each patch is in roughly the same hairless location on both arms. It's very odd looking.

The second is a wide scattering of what appear to be more like traditional pimples, but which are also quite large, and also haven't gone away this entire time. They're very red, and some have an light amber tint to the center, as if filled with pus. They hurt and itch. I've gotten bodily acne before in the summer, but these seem different in that they're very tall and rounded, without the wide red base that a lot of "normal" pimples have. These also are not around hairs.

I've been very strict about cleaning and moisturizing the area, and I don't wear any shirts that even extend down far enough to reach or cover the area.

My dermatologist -- who, it should be noted, I am not overly confident in -- was only willing to take a passing glance and was dismissive. There's a slight possibility that I recently developed HSV elsewhere (awaiting more test results) during a period of low immune response, but I'm not sure that these symptoms are all that consistent with a spreading of that condition, especially given the amount of time involved. Still, the clustering and identical locations (maybe at the end of certain nerve pathways?) make me think that it's at least worth mentioning.

Any ideas as to what this is, exactly?