This really isn't that uncommon—I think most people find it easy to give advice, but it's much harder to live by it yourself!
If you're really finding it that difficult to help yourself, try imagining that you're helping a friend. What would you say to someone else in your position? Sometimes, just imagining it's somebody else's problem helps you to detach from it emotionally, and allows you to solve it more logically.
Confidence can play a big part in this, too. It's easy to tell someone to just talk their problems through, but when you're the one with the problem—and it's your partner you could be having a difficult conversation with—it's much easier to just avoid conflict.
The same goes for telling someone that you like them. Nobody likes laying their heart on the line and risking pain, even though it's usually worth the risk!
It is possible that you're having trouble helping yourself because the advice you usually give is useless, but that's probably not the case—your friends wouldn't listen to you if it was!