im so sorry you're feeling this way. if you get a chance, read through this book http://freepdfxdownload.blogspot.co.uk/2012/07/free-pdf-overcoming-obsessive-thoughts.html
ive been through this, and i was exactly the same as you, always falling for the guy in the movies, dreaming about when it was going to be me, but when it came to real life, i was terrified about boys. i didn't know what to do or say, they were completely foreign to me and the thought of dating a real one made me scared to be quite honest because i didnt know what i was doing. my first hit of hocd was when i was 16 like you and it hit me like a tonne of bricks just suddenly one question that i couldnt let go of 'am i gay'. terrifying and horrible. its like my brain brought back random memories and events from my past as proof it was hard not to just believe it. the one thing to remember is that ocd is all about uncertainty and fear. and the only way to get over it is to understand and accept that you cant have 100% certainty all the time. the reasons these thoughts come back again and again are because you're giving them a meaning and substance when you get fear from them if that makes sense. the best thing to do is laugh at the thoughts, agree with them and just answer every question with a 'yeah that's right im gay'. i know that sounds like the opposite of what you should do but believe me it works. strip away the fear and the thoughts will go too. i was exactly like you, i felt as though i had to act and be completely straight or else i wasn't. when i was younger i even thought that i couldn't even acknowledge that a girl was pretty because that was what lesbians did/thought and i wasn't one! im slowly learning how silly that was and laugh at it. i hope this helps in some way!
I agree with 123tushar07. One can't stop Prozac without weaning off of it. It can cause problems by stopping it. I'm so sorry you are feeling this way. You do need to see a doctor and tell them what is happening. The doctor can help you. I hope you have someone you can talk to about this and get care ASAP. I think that many people feel the way you do. Some to a lesser extent, some to more. Take care of yourself.
Dee
I think you need to take proper treatment for a longer time than you have taken, you have taken only one session with therapist and also you stopped taking medicine on your own.
you need to take the treatment seriously otherwise ocd can make you feel disabled in every aspect of life. I think you need to start fresh in your treatment, you should see a psychiatrist.