That is not something you want to wait on. I don't want to scare you but you could have a clot that is waiting to become an embolism. Does it hurt when you flex your calves or walk or has any area become red? If so you don't want to wait to see a doctor. You should go as soon as possible. It might just be something simple but you never want to take your health for granted.
Best wishes, I hope for the best for you.
It could also be gout or something along those lines. Poor circulation can cause swelling too.
You could have water retention or maybe you have inflammation in your joints. If it persists i would definitely get checked by the doctor. I would also see the doctor when it is swollen. If you go when it looks normal if is harder for them to get a picture of how it looks and then it makes it harder for them to understand. But if you can't get in right away take a picture of how it looks swollen just in case in goes down by the time you see him/her. I am speaking from experience!!!