It wasn't meant to be and there is nothing that will allow you to change that. The worst thing you can do is worry and become upset because you are not able to force others to like you. What you should do is hang out with the guys; go play football, baseball, & video games. Anything to allow yourself to generate a new routine. Once are able to allow the day to be filled with new hobbies and interest, it will be easier to get over the rejections. PLUS, she is the one that is at lose, not you.
I don't think often of whether I am happy or not. Happiness is only an emotion..I do not trust my emotions much! I am ok at being content. I take one day at a time, doing the next right thing. When I feel happy, I just thank God for that fleeting moment. When I feel sad (another emotion I do not trust), I usually do things for other people. That gets me out of me! Ha! I really am sorry for what you are going through, and I hope you are soon okay again!!! :-)
They say boys deal with rejection better than girls... Since they are usually the ones to ask out girls they get better at dealing with rejection... It's not like you were in love with her, it was just a crush, so you just eat a burger and move on to the next pretty girl! Trust me there are plenty out there...
Read the serenity prayer. It will answer your question. If you don't read it, just know that it's the girls loss, your gain, because you're free to accept someone way better now than that girl ever was!