Husband won't have sex with me

I've been on my period for 4 days and am super horny. We've been together since high school (over 6 years). I asked my husband to make love to me while I'm on my period and he said no. It's never been an issue before and it makes me feel horrible about myself since I just got it back after having our son. I just want to make love but he says it's gross now. How do I bring the issue up for conversation? Any ideas as to why this would be an issue now? We've never had trouble communicating before but lately everything's been a fight and I've been sleeping on the couch...