What Should I Do About A Sore At The Entrance Of My Vagina Which Causes Burning Sensation?

Hi, please i have a sore at the entrance of my vaginal after childbirth which gives me burning sensation whenever i urinate or it come in contact with water. It s getting to 5 months and it s not healing. I use amoxi 625mg last month but no changes. Please what can use to make it heal