My akita is 9 years old, and healthy, but today, started yelping and not using his hind legs as much as he usually does. Took him for a walk and he did well, but when we got in, if I wanted him to lay down, he wouldn't.

Time for a vet check.
There are many possibilities as to what could be wrong, anything from a pulled muscle to hip displaysia.
Vet will more than likely have a feel of the legs and possibly do an x-ray of the hips.

I second the pet motion. Unfortunately there is just too many possibilities here.

Thank you so much. Took to the vet today, was a pulled acv or something like that... muscle.

Glad to hear you took her in!

Hope for a speedy recovery :)