Have Cat Questions? Ask a Cat Vet Online.
The general rule of thumb is that if pain lasts longer than 48 hours, you need to see the vet to find out what's going on. It might be more than just a sprain and, if so, you need to get anti-inflammatories and supportive therapy from the vet.
There are no over the counter medications that are safe for cats so be sure that don't try any home remedies, except for ice and heat.
Let me know if you still have questions.