why don't you get screened that lump to find solution. If it is not troubling you then no need to worry. stay calm and relax and if it is troubling you, you feel pain or some thing then you must not have to waste time
While it's normal to be worried, I would try to relax. Naturally, I would suggest seeing a family DR (or - a dermatologist) for the reason that it would be impossible for someone to guess at one it is based on your description.
But - being a guy myself, our changes in weather this time of year, and considering the location which is usually confined by clothing and doesn't receive much "air circulation" as, lets say - the back of our hands, I would have to question if it's an in-grown hair or a cyst (which is similar to a pimple - just not so close to the skin). If that's the case, it'll probably be tender or sensitive when you touch it.
If you think it's one of those two things, I'd probably soak in a bath for a half hour before bed - and following that I would mix "Epsom Salt" (which you can buy at most groceries, drug stores, and dollar stores) with just enough water to make it a paste. Place the paste over the bump, cover it with a band-aid so the paste stays there. That remedy usually helps me with similar problems.
But ... ultimately ... I would try to minimize worrying, I would get to a DR - they'll know how to take care of it most quickly and your mind will be eased.
J