I am deffenitaly not pregnant bc I am still a virgian but my breast r very sore never been before?

Your menstrual cycle can be drastically effected by weight if you are under weight or incredibly over weight then your cycle can become pushed back or can even stop all together. Your menstrual cycled is your body saying it is healthy enough to support a developing child so it would make since if you are very thin your body then your body feels it is not healthy enough to have a child. Although I would still recommend seeing a physician.
The sore breast can be explained by what most would call "growing pains" although in a different area. Tenderness is most likely a side effect of your breast increasing in size as the tissues and milk sacks are developing further. Sore breast could appear before the menstrual cycle or after. To help I suggest try a bra with more support and also bringing it up at your next trip to the doctors, it never hurts to check.