Hello dear
Understand your concern
I think it may be due to rough sex or post menopausal state due to estrogen deficiency
Following are the other cause of your problem:
Endometriosis
Endometrial dyspalsia
Cervical dysplasia
Dysfunctional uterine bleeding
Fibroids/Adenomyosis
PCOS
Hormonal imbalance.
For exact diagnosis you should consult the gynecologist and require  following investigation
Pelvic examination
USG
endometrial biopsy
Pap smear
Ovarian follicle study
Take meftal spas
Drink more fluid
Eat healthy diet
Limit caffeine, salt and 
nicotine Healthy lifestyle 
Stretching and regular exercise routines will reduce cramping and 
menstrual pain.
Yoga can be extremely helpful to reduce both the physical and mental symptoms 
Massage can also help both physical and emotional symptoms. also relieve 
depression, anxiety and panic attacks.
Hot baths help with cramping, 
back pain and relaxation.
Sleep of at least 8 hours
Keeping The Vagina Dry (Not wet, clean well)
Wear pure cotton Loose underwear
Best regards
Dr. Sagar