Hi there what is wrong with me i'm am wearing girls underwear and fantasy about my sister to?

Doctor can evaluate: A guy in his late 40's who is wearing girls underwear and wondering about his choice of clothing can see his primary care doctor for evaluation. His primary care doctor knows his whole picture and likely has seen the patient regularly for several or many years. A referral to psychiatry may be done if the doctor and patient decide that might be helpful.

Uncertain: There really isn't a way to assess you after receiving a one sentence description. There are at least a couple of reasons that a man might wear a woman's undergarments. You haven't told us if wearing women's underpants and fantasizing about your sister primarily upsets you or primarily makes you feel good. Recommend assessment by a clinical psychologist to look at the big picutre.