It sounds like you have what we classify as secondary amenorrhea, and I recommend discussing this with your OB/GYN. This is simply when a woman's period disappears after having it at one time in their life. There are many causes for secondary amenorrhea. The most common cause by far is pregnancy. If you have never had intercourse, this is off the table. The second most common cause of secondary amenorrhea is hypothalamic dysfunction. This is a problem with the brain's hormone center that usually occurs when someone has been very physically active or has lost a lot of weight recently. The third possibility is a polycystic ovarian syndrome which I think you are eluding to when you are describing your lack of abnormal hair growth. I really can't think of a common cancer that would cause this, though you should definitely get that lump checked out.
The best type of physician for you to see about this problem is an OB/GYN. They have a very standard workup for secondary amenorrhea which will likley include blood work and potentially a pelvic ultrasound
. If you have started a new sport and are working out a lot, your doctor
may just ask you to take it easy for a bit and your periods are likely to come back (if that was the problem). Good luck.