What do you mean by "motivation"?
The thing is, if I want something to happen, then I'm motivated to make it happen, and if I don't want something to happen, then I'm not. If you're not motivated to do something, and you think you want the result, look deep within yourself and question what it is you really want.
Let's say that you "want" to become a very rich person. Then you look at what you need to do to achieve this goal. It involves a lot of dedication of time to potentially boring or even degrading tasks, and a sacrifice of years of your youth in order to achieve this monetary goal you've set for yourself. When you look at this future that you need to acquire your goal, you may lose your "motivation". But is that really a loss of motivation? Are you not just weighing the potential rewards of this kind of lifestyle and saying, "hey, maybe doing all this bullshit to get more money is going to in fact lower my overall happiness instead of raise it, so maybe I'll look at a different option"?
I don't lack motivation, I only focus it in particular places, which others may not find worthy of someone's motivation. I do, so fuck them. It is possible that you've not found something worthy of putting effort into. That's fine. You can't change what you want, period. Don't let other people's expectations of what you "should" want dictate your life. Aspire to only what you find to be worthy of aspiration.