Not able to have a orgasm

I am having a difficult time to reach a orgasm when having sex with my wife. I have to use a combination of Viagra and a pump with a ring to have a erection good enough to have sex. The problem is that I start out having normal sex and great feeling of building up to a orgasm and then the feeling goes away and I don't have one. It's quite frustrating and my wife feels guilty that she isn't doing something right. That's not the case I tell her, you're doing everything you can. Has anyone had this experience and if so, have you had a remedy or still suffer from this issue? I have had the same problem when using Trimix.