For one thing, artists seem to run on hyper mode a lot...there's a flash of inspiration and then the compulsion takes over until the piece is finished. Do that day after day, with the rest of life thrown in there, and it can bring you to the brink of physical and mental exhaustion.
So you need to take some time for yourself to rejuvenate. Not everyone is a nature person, so maybe a nice long soak in a tub or a quiet moment at a favorite spa will do it for you.
But for me, I just force myself to take 10 minutes out and go sit outside and just turn it all off. No trying to figure anything out...just look at the clouds, listen to the birds and chill. And the funny thing is that once you've done this things just start to flow...ideas for new work just seem to spring from nowhere, and it's because sometimes creativity gets trapped by all the noise in your head and it needs a quiet moment to be heard.
So try it...10 minutes agonizing over why ideas won't come, or 10 minutes to just relax...even if the creativity doesn't flow you've given yourself a break that was much needed and deserved.