A few years ago, I started to feel the same way [restricted], where it got to the point where I went to the person I used to talk to for advice and asked "Is it Halaal for me to be happy?"
He didn't give me a straight answer (idiot :P) but he should have emphaticaly answered "yes!"
You see the reason that folk like us have this problem is that the texts (Qur'an and Ahadith collections) talk about progress. How to be better people and more sincere worshipers. What they don't explicitly discuss is, being happy and having fun. They discuss this, but not explicitly.