28 year old female virgin with no interest in dating/sex. What is the reason?

Evaluation Needed. There are multiple possiblities. Would be interested to know more about your medical and developmental history as this could be related to physical and/or psychological causes, including hormone deficiency or presence of other medical conditions. If you have not done so, an evaluation with a primary care doctor would be a good place to start in order begin to understand the root cause.