Husband avoids sex

I'm so sick of when I try to have sex with my husband and he gives some excuse that he doesn't want to. Now, don't get me wrong this doesn't happen all the time, but when it does happen it makes me feel like an idiot for even trying. What kind of husband doesnt want to have sex with their wife! I never turn him down. I never thought it was possible for a man to have a lower sex drive than a woman.