Help with my rhythm please
 

Hey there! Please forgive me if I am posting in the wrong thread, I'm brand new to this site! I've been playing guitar for about 6 years now and I know a good bit. I love playing around bonfires with my buddies and singing good ole country music, but there's a problem... I have great rhythm on my guitar, as long as I'm not singing. When I start singing it's like I don't have enough brain power to make myself sing and keep a strum pattern going. It seems like a mental block to me and I cannot get past it. Does anybody have any excersizes or advice for this problem? I feel like my songs would sound a whole lot better if I could have rhythm in my strum hand while I'm singing. Thanks! And again, please forgive me if I am in the wrong thread!