Try to find out whats bothering yourself and be honest about it. Could be family, health, stress, you find out you hate holdem but still want to be good at it, lol, it could be anything. Best thing is to find the source of killing your motivation to play.
But if you're stuck on playing holdem then something that works for me is paying attention to how many
hands I play and how active I am in those hands on a daily, week, monthly basis. So first, find out how many hands you normally play in a day or a session. You should be able to know that by a hand history or if using a tracker than that's uber easy.
For example, if you normally average playing 200 hands everyday for weeks or months then all of sudden bump it up to 350 a day then that might drain you. The next part which is a little more difficult is rate how active you're in those hands.
Lets say you avg playing 200 hands everyday but all of a sudden you change from playing a tight aggressive game where you fold more to a looser style that requires more thought, stress and attention then its going to drain you faster but its still playing the same 200 hands.
Something else you could do if you still want to play poker but you're getting sick of playing Holdem is to try another poker variation like one of the games in 8 game to mix things up and come back to holdem later or just take a break from the game like so many folks have suggested.