Is something wrong? Might be TMI...

My husband and I have been TTC for over 6 months now. I think our main problem is not having sex enough especially during my fertile window. I would have sex every day but he physically can't. He can only go like once every couple to three days. It's not that he doesn't want to bec he gets hard etc. but there's no big finale (if you know what I mean).  I feel really stupid but am I doing something wrong? Or is it something with him? Btw, He drinks a lot of water and/or lemonade.. I know that can affect things. Any ideas, ladies?