Not having enough sex

My hubby and I barely ever have sex anymore. It's not me, I'm always game! But he says he's always tired and lately I'm lucky if I get it twice a month. I've tried pretty much everything possible to get him in the mood but he keeps either rejecting me or falling asleep. I know he's not cheating, but he is under some stress but this is ridiculous. I don't even try anymore because I'm sick and tired of being turned down all the time. Any advice would be appreciated. Thanks ladies