I think what often happens is that a pore is blocked and fluid collects under it, like serum instead of sebum.
It can be a mole. A mole can grow anywhere. Just leave it as such but keep an eye on it. If you notice changes in the mole's/mark’s color, height, size or shape, you should have a dermatologist evaluate it. You also should have it checked if it bleeds, oozes, itches, appear scaly, or become tender or painful. Otherwise it should be left as such.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.