Getting dry during sex...help??

*long winded I'm sorry*
So, I'm in a healthy monogamous, long distance relationship. So obviously we only have sex when we see each other which is typically anywhere from 3-6 months just depending on how life is. And when we do, we typically have a lot of sex (at least once a day or so), sometimes for short periods of time and sometimes longer. 
Well, I've been feeling myself start to get dryer faster and I don't know why. I used to be able to go three times a day for longer times and be fine and still be able to do more the next day. Now I can do maybe one longer round and even during that I get dry. It's not that I'm not enjoying it either. And there's no condom getting in the way. 
Can anyone help me out??