Firstly, you are in no ways alone with this problem and your doctor should be most sympathetic, but by all means request a female - I am sure they will understand. As you will appreciate, there are various degrees of your problem and although it could be a long time of treatment, most likely the therapy will get results very soon.
Obviously, you will also appreciate that as you give little details of yourself, it is difficult for anyone to give advice from personal experience. As you say that "you fear you have a problem", then that problem could largely be the result of fear of the problem. Whilst in no way condoning under-age sex, we all know it happens. And we also know that many young girls are under pressure to act as their friends do (or as they say they do!), then if this is your case then that very pressure can bring on your condition.
Both Males and Females suffer badly from a fear of not being able to perform - that results in a tenseness - that results in difficulty and so on in a viscious circle.
I only wish I could offer advice applicable to your personal condition.
Anyway, take heart in that you are not alone and the many many other fenales who have initially suffered as you and the numerous men who have had their own version.