My little girl was spayed on Monday and was in quite a bit of pain as well. The vet did send us home with some pain meds to be given 3 times a day. They seem to help but they knock her out. She's been sleeping a lot, which is a good thing.
They also told me to keep her from licking her incision so I purchased a premie onsie from WalMart and it fit her almost perfect and completely covered the incision. Having the onsie buttoned around the toosh also prevents her from doing much jumping.