Hope it's not too late, but it sounds like he has ick. What's the temperature in his tank? These guys always tend to get sick in the winter because the temp drops. Try cleaning his tank first. Whatever the temperature is right now, raise it one or two degrees. Anymore than that might be a shock to him, but one or maybe two degrees should be fine. Do you have aquarium salt? Not table salt. Aquarium salt. If you do, you should add some of this to the water. You didn't say how big his tank is, but if you have aquarium salt, the side of the package should tell you how much to add. Make sure you stir it up and disolve it really well so he doesn't get a salt burn. If you don't have aquarium salt, go get some. It only costs about 2 dollars and will last for a long time. Then keep looking at the temperature. How cold is it in your house/apartment? He needs to be in a temp somewhere in the 80s. The warm temps really help. Try to SLOWLY raise the temperature of his tank over the next few hours. Maybe put his tank near a lamp. This should help right away. If not, then try some Betta Fix. Again, only a few dolars. Follow the directions on the bottle.
Hope your little guy turns out okay.