I'm glad you talked to the vet. That's who is going to be able to help you the best.

Several years ago I found my cat limping one evening. He was also whimpering in pain. It was very scary for me. It was a weekend evening and the vet's office wasn't open so I paged the vet on call. We determined it was his knee. Not sure how it happened but the vet thought maybe a jump that went bad. The vet said it didn't sound like it was broken and would probably work itself out by morning. Fortunately it did otherwise we would have had to go see our vet the next business day.

Hope your kitty is better soon!