Problem orgasming over men?

I've always been bisexual and never had any problem orgasming over both sexes. But ever since I started taking Prozac in the summer, it's virtually impossible for me to orgasm over men. One of the side effects is difficulty to orgasm except I seem to have no difficulty with it when it comes to women! Me and my boyfriend often masturbate together over Skype (LDR problems) and it's always so embarrassing because I've never been able to orgasm for him. One time I'd been trying for a good half an hour and was no closer to finishing than when I started. Do any other girls have this problem? Even if they're not bisexual. I'm becoming really confused as to why this is happening.