Sometimes it can be tough to find the strength to keep exercising. For me I find the best way to stay motivated is not to think about my current self or my self at the gym but to think of myself after the gym. When I think about my goals and what I need to do to accomplish them it can help push me the extra mile. Also it can be a good idea to have a workout buddy, for me this is my girlfriend if I ever get lazy about working out she gives me motivation by reminding me of our goals. Find your motivation.