I been struggling with my weight my entire life. no matter what strict diet and how long i exercise. and my tests come back normal. what could it be?

Obesity: is really hard to deal with. It's more of a lifelong struggle that needs to constantly be battled with. What I can tell you is that there's no quick fix. You need to make lasting lifestyle changes (that are maintainable). Seeing a nutritionist is a good place to start. Set a target weight and then make a plan for getting there. Best of luck.