I think it could be anxiety related as sometimes i feel anxious in other parts of my life. But if it is anxiety what can I do to fix it?
My first thought is that you are much too young to need Viagra and quite possibly it's the Viagra that is getting in the way. Since your organs are working properly during masturbation, a kind of performance anxiety may be overtaking the situation during intercourse. Cut out the use of Viagra, involve plenty of foreplay, and let your body react in a natural way. If you have a partner, also avoid all masturbation, carrying out anything sexual with that partner, so that all of your sexual energy will be available.