Everyone is busy now-a-days, making it easy to kid yourself into believing you just don't have enough time to get important things done. Especially things that take a lot of time.
For years I struggled with doing whatever interested me but never really accomplishing anything of substance. I could do a lot of things, but I never really had anything to show for it. This in itself is not a bad thing. However, if you actually want to get something done you need to start and finish. This requires focus.
Doing something of substance usually requires a lot more effort than you expect. If you are committed you'll push through it. Being focused is more and more difficult given the constant distractions of apps, phone and Facebook. Do any of us really know what it's like to be focused vs. just busy anymore?
If being focused is important to you, it's actually easier than you think. Just substitute whatever you'd do when you do nothing with something - the same thing. I call this a default activity.
What is a default activity? It's that thing you do when you have nothing else to do. Is it an activity that will get you what you want out of life?
The default activity for most people is to watch TV or play games. This is probably not going to get you what you want, it will certainly waste your time. Being very busy, you need some relaxation time of course, but playing Candy Crush for 5 hours a day is probably a bit of overkill.
Fact is, you are probably tired because you've just spent all day doing stuff you needed to do vs. what you wanted to do. It took so much effort that you need to "relax" to "take your mind off it".
In reality, doing something you like to do is energizing. So, why not do "it" whenever you have nothing to do? Chances are you're not doing what you want to do because you don't know what you want. This is a common problem.
What is the "it" that will get you what you want? Identifying your "it" is not easy. "It" needs to be something you are willing to do a lot, even when you are tired.
I can't tell you what "it" is for you. All I can say is, you can figure it out if you make something a default activity for a while.
Let's say you want to be an author. Instead of watching TV, you write. Let's say you want to make a lot of money. Instead of playing games, play the stock market.
Eventually something will happen. You'll either accomplish what you wanted to, or you'll go back to playing games. If the latter happens, pick another default activity.