Always worried when I find strange bumps/rashs on my junk
Yeah often times when I get red bumps on my penis, it's just an external irritation, not an STD. For example, I had a single red bump that would become more red after sex but mostly be invisible. It turned out, that the inter-netting in my swim trunks were abrasive (cheap) and caused this mere irritation (contact dermatitis). Certainly had me worried at first.
Contact dermatitis - "Some rashes look like an allergic reaction but really aren't, because your immune system wasn't involved. Instead, you touched something that took away the surface oils shielding your skin. The longer that thing stayed on your skin, the worse the reaction. It's called irritant contact dermatitis. ".