I've been having a similar problem, and I am trying to get back to my former interested and motivated self (about the things I used to like and lost interest). I'm not sure how to do it properly yet, but I reached the conclusion that it is merely life that changes us. We don't have to stay where we used to be, and it is ok to change direction, interests etc. It could also be a mild depression, early mid life crisis, sloth, being tired of things, whatever (not talking about you, just in general). There could be many reasons, so in order to find the solution we should identify the cause. In my case it's a combination of all of the above, but I keep in mind that it is my life and if I want different things than before it's fine
I do have negative feelings thinking that it's like giving up, wasting all my past efforts, but in the end nothing is wasted. Experiences are all with us.
I hope I don't speak out of place, I am just sharing my small experience on the matter.