It's possible there's some physchological aspect. Did this happen during your wife's first pregnancy?
In the meantime here's my advice.
You know your PC muscle? ITs the muscle you use when you want to stop the flow of piss. I recomend taking a piss and then start pinching it off near the end of so you get an idea what muscle I'm talking about.
Now that you know what muscle it is I'd like you to squeeze and release that muscle about a 100 times a day to start off. Make sure you squeeze it as hard as you can and only release it for about 2 seconds.
Now I want you to get a hard on. Squeeze that muscle about 25-50 times.
Now bring yourself near the brink of ejaculation and squeeze and hold that muscle till the urge to come goes away. and you start to get soft a little bit.
Now repeat. You should repeat about 3-5 times.
the most important part is not to ejaculate.
Now when you finally cum you should feel something.
[Link]