And this bump is new? Or you do not know if it is new? It is quite possible that the vulva floor is bumpy and not smooth. This is normal.
There are two glands, one on each side of the vaginal entrance, the Bartholin glands. Sometimes one can get blocked or develop a cyst. It will form a pea sized bump that can evan be felt through the outer lips. Soaking in warm water can help unclog it if that is the problem.