It started with a pimple on my elbow. then i feel a lump inside, as if it is stuck on my bone. there is no pain, the lump is also not visible yet but the area is pinkish. what is this?

Good Evening: There is several reasons why you could be having this issue. I would like to see a picture to have a better idea how this looks like. Has it changed in color or size, does it itches or burns? One possibility is that you had a previous trauma that created a callus on the bone. If you could explain with more detail when and how it started i could help you better. I recommend you to have an x-ray.