Dog Constantly sitting and now hurt tail?

About 2 weeks ago one of my dogs started sittings randomly. A lot.
She would walk around and sit, get up and then sit immediately again. Lick the air sometimes.
Now her tail is hurt from it and its flat, it wags but it doesn't stick up in the air.
I thought I narrowed it to Two option, she had worms or her anal glands were full. I figured she didn't have worms because she hasn't lost any weight and eats just as often and none of the others have started this. I tried taking her outsite and "expressing" her anal glands a few minutes ago. There was either nothing there or I could not find them.
I don't know what to do now. I don't have the money to take her to the vet ATM and it doesn't seem like a really bad problem or injury...last time I took my dog to the vet for a "SPRAINED ANKLE" and it cost be 1400 dollars.

does anyone have any ideas or experience with this?