Hi,
Welcome to the ehealthforum and I am really glad to help you out. The vagina and vulva are delicate, yet resilient structure made of skin, mucous membranes, muscle and so forth. The lining of the vagina is very similar to the tissue that lines the inside of your mouth. It's soft, squooshy, and it bleeds when it's cut or roughly rubbed.
Doing masturbation in a rough manner can lead to tears or injuries to vagina or cervix(if there is deep penetration). In future,do masturbation gently and at a comfortable pace . If anything hurts, stop and readjust till it's comfortable. Masturbation should be performed on your back, although you can try it sitting or standing once you've learned it on your back.
If symptoms persist then any fragile growth on the cervix or vagina like a polyp needs to be ruled out. A pelvic examination and ultrasound from a gynecologist then needs to be done.
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.