Worried I’m accidentally rude

I’m a very anxious person and I work at a large retail store. It’s such a big store that I don’t really know more than half of the people I work with, so it can be so hard to tell whether I should just keep going about my work and say/do nothing, or if it’s rude not to smile, acknowledge them in some way? Seems like it shouldn’t be so confusing, but many people don’t respond or look weirded out when I acknowledge their presence, and so I’ve gotten so annoyed with it that I’ve stopped altogether unless it’s someone I work with regularly. I feel like there’s some social code for this kind of setting that everyone else understands and I’m just awkward as hell. Am I overthinking this? Any ideas/tips? Thanks