This could be depression. It may be time for a med adjustment. I'd call your pdoc.
The other possibility is that you are not on a course in life that you really want to be on. This is what happened to me. I was going to enter the family business selling life insurance. I could not for the life of me motivate myself to work. This was when I was in a normal mood cycle too.
I'm convinced that I didn't have motivation because my higher (subconscious) self just really didn't want to sell insurance. I finally had to face facts and admit to myself that I simply couldn't motivate myself in this line of work. I ended up getting a sales job at a shoe store that paid hourly. There is no motivation needed for that kind of job.
I worked that job until one day I had an epiphany. I realized that I wasn't going anywhere in life, and since I couldn't motivate myself to do something I didn't want to do, I had nothing to lose by following my heart. I have always loved to write. That was the path I would follow.
So I began to research ways to make a living writing while I was still working at the shoe store. I came across a novel type of writing that I had never heard of before: copywriting. Copywriting is basically writing ads and other sales materials. I got a book on copywriting, and it was super interesting. I started to study in my spare time while still working at the shoe store.
I found that I had motivation to work now. I really believe it is because my subconscious wanted a creative outlet. It is known that bipolar people are highly creative. There have been a lot brilliant bipolar writers, musicians, actors, actresses, and artists. In my opinion, I think it's very important for bipolar people to have a creative outlet for their inner creative energy. I think if someone doesn't have this, they will suffer depression.
Eventually I was able to quit the shoe store job and be a freelance copywriter full time. Anyone who is interested in becoming a freelance writer you need to this book: The Well Fed Writer.