Ughhh.....I sound like a guy?? Why do I have such a deep voice...it's embarring?

For some reason on some days my voice sounds deeper than others...most of the time I sound like a girl (which is good cause I am one) but today if you only heard my voice you would probably mistake me for a guy. It's frickin weird. What do I do? I'm not congested or anything...so I have no idea what the hell is going on. What should I do? It bothers me more than other people because I'm a singer and well I don't want to sing if I sound like a dude on certain days. Any advice?