Hello,
Without examination, confirmation of a diagnosis is tough but it can be folliculitis, contact dermatitis,rash due to friction rub with clothes, dermatitis (atopic, contact, allergic),excessive sweating causing sweat dermatitis or balanitis(due to an underlying infection (bacterial and fungal as well as other organisms) .Even genital warts cannot be ruled out as it is spread through direct skin-to-skin contact during oral, genital, or anal sex with an infected partner.
I sincerely advise you to consult a dermatologist and get yourself evaluated for these possibilities.
I hope it helps. 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 and please do keep me posted on how you are doing.
Only a physician can answer your question. However, the vagina is very sensitive, especially when on medication. It's natural balance is not working properly, most likely due to meds, which can irritate the skin (area) enough to have it slightly blister or bleed after engaging in sexual actions. Just a possibility....