Your strength is very impressive, even for your height and weight considering your age. It sounds to me like you've hit a plateau and the amount of weight you're pushing is taxing your muscles pretty hard. I'd stay away from test at your age, but instead look at trying different workout routines and finding a diet that focuses primarily on recovering damaged muscle fibers. There is a good chance that your workout routine is producing more cortisol than growth hormone at this point. I would seek out lifting routines that are designed to do the opposite.