That's something to think about. I've been always struggling with the same as you. At first I got a lot of energy to embrace a new project, then few weeks later I tend to lose interest. I've found out that discipline is the key, and only by exercising, riding my bike, getting up early, and getting fckd up in bjj classes that my mind got back into place. Nothing in life comes easy, and if it does there's something wrong. I'm learning to love pain and discomfort, for I know it's the price of good results and great achievments. It's some kind of evolution thing. We as an species evolved to get protected by all costs from any harm, and the result is that most of us are lazy mthfkrs. One way of dealing with this is the following: when you don't feel motivated enough to go to the gym, per say, that's the best day to go out and smash it, because before you go you'll have to fight your most important enemy: your ego.
Perfect. That's it. We have to learn to love discomfort, I keep learning, I keep doing what I must to achieve my goals even if I don't feel like it. Strength for us!