The most likely reason you feel unmotivated is that you are in a lousy state of mind. It can be caused by various things, like:

Forcing yourself to work is like swimming against the current. You'll need a lot of force to get to your destination.

For the moments in which you don't feel motivated, try to change your state as quickly as possible. The longer you wait, the harder it’ll become.

You can produce motivation at your own command if you understand how it works.