What Causes Vaginal Pain And Heavy Periods After The Birth Control Shot?

hi I have been on a bc shot and It made me period go crazy so I have been wearing pads for 2 and a half 3 weeks. My vagina has gotton very irritated from it. It was very itchy and sore and I believe it has a cut or it cud be from me scratching I dnt know..I know It cant be no herpes or warts because there are no bumps or nothing around it plus I alwasy use condoms could you please tell me what the problem is??