I got 3 fill-ins the day before yesterday. Both cheeks are swollen. And my jaw is sore. This is not normal for me. How concerned shouldI be? Should I go back immediately?

Concerned. If you had no cheek swelling yesterday, and no jaw sore yesterday. Call dentist now. He/she may want to see you today.
Very common. If it does not resolve in time (1 week) and gets worse then see your dentist for evaluation.