Look at all the things you eat and see where you can make an improvement in the quality of food. Then really figure out the quantity, it's all about calories and timing of your meals. You could very well be exercising too much and not being able to stick to low enough calories because of that, thus overeating 100-200 calories here and there and it all adds up in the end.
I would not wait to gain more before I did something.
Good luck
