My Old English Sheepdog started to limp today, advice?

Today my female OES started limping today after not really doing anything today. She was fine yesterday, but today she favored her left hind leg. She doesn't seem to be in pain, and was actually trying to jump around and run when we took her outside. I laid her down and tried to find the source of her discomfort. When she laid on her back her, she was able to lay with her legs open, but she kinda cried when I attempted to straighten her leg. She is not over weight( 47lbs) and pretty much sleeps all day. I can't take her to the vet until Monday. Any suggestions other than taking her to the vet?