If the smell mostly reminds you of bad BO, it could trichomycosis axillaris. It's build-up of a common bacteria that feeds on hair shafts in sweaty areas. If you image search this, you're going to see some extreme cases, but even minor cases are stinky.

Look closely at some armpit hairs under a bright light (pulling them up or just plucking one out). If you see any semi-transparent, waxy build-up at all, anywhere on the hair, that's probably trichomycosis biofilm. All you have to do to treat it is keep your pits closely shaved for a few weeks to starve any colonies clinging to the skin. Improvement in body odor should be immediate.