I know you're sick of being sad, but there's nothing wrong with being sad for awhile...a long while, a short while...it's normal. If you weren't sad, that would be abnormal!
Going out and trying to have fun really REALLY sucks when you feel this way. I've been there, and I'm sure pretty much all of this board has been there too. Personally, I like to rent some cheesy (but definitely non-romantic) movies and maybe invite a close friend over to watch them with you. And cry! Crying is a big release when you feel this way. Buy yourself some chocolate (if you like it...if not, then get yourself some kind of treat that'll perk you up). Just don't go out and get drunk. You'll feel like crap (because chances are, you aren't sleeping or eating as well as you would if you and him didn't break up) and you might end up doing a drunk-dial, which is never classy.
Another thing that's a release is to do something different to your hair. Maybe get a cut, or lighten it a little. A LOT of girls do that after they've been dumped, and it's a confidence-booster plus makes you look a little different so you feel a little renewed.
Feel better, babe. We've all been there, and you'll get through it at your own pace!