It's one of the biggest problems I'm struggling with. 
How to motivate yourself when even the things you used to like don't bother you anymore? 
When there are no things to look forward to and nothing that interests you anymore? 
When doing nothing seems better than the alternative, but at the same time doesn't seem better at all? When every little bit of effort makes you feel stressed out and exhausted to the point of giving up?
I wish I had a clue. 
I keep searching in hope of finding some answers but I'm not too optimistic. 
Even advice that is supposed to motivate tend to have the opposite effect on me. 
But perhaps this is how life is supposed to be. 
I certainly wouldn't hope so because that would mean that life is just suffering to me. 
Something which I could never accept of course. 
I hope you can find the answers you're looking for.