I'm not sure what you do, but I know that I have a bad habit of denying compliments. However, I'm trying to be conscious of that and accept them when they come my way.
Maybe you just need to believe them when you get them. If you feel low about yourself, you're less likely to accept something that's going to make you feel good because you think you don't deserve it. Next time someone compliments you, just smile and say, "thank you," and you'll make yourself feel nice, and make the giver feel good, too.

It's a difficult lesson to learn, no doubt, but you'll get there!