How Can A Vaginal Lump With Swelling During Periods Be Treated?

im 27, height 5'3, 120 lbs. im a mother of four kids. all of them was born at home only.after i gave birth to my youngest 3 yrs ago,i had these lump in the entrance of my vagina and it swells every time i had my period. and my right vulva did not return to its normal. whats this?