Hi freewill,
I remember feeling the same way. Ask yourself if it is loving to sing a happy birthday song or an unloving thing to do. Are you worshipping the day or putting your husband above God by singing? Whatever is not from faith is sin, that what it says in Romans. Pray about it and ask God if you would be sinning? I did. I asked Him all sorts of silly stuff. I'm surprised He put up with me. lol. love, dj