Why do I have pain when chewing three weeks after fillings?

You had a lot of dental treatment, so any discomfort that you feel may be normal in the short term. When any type of filling is done, the bite is usually what is off initially. That should be checked first. Since you had tooth colored fillings placed, sometimes teeth are sensitive from the bonding process. This takes time for the tooth or teeth to heal on their own. Have your dentist make sure the bite is good, then wait to see if the teeth heal. May need to give it a few months.

This is a common problem, that bite sounds like it could be off especially with all the work that had been done. You did not say the fillings were deep, but assuming they were not that is the likely scenario. Call your dentist and have them check and adjust the bite. Sometimes it does take time for them to feel better.

Time won't help. You need your bite/fillings adjusted as soon as possible. Waiting for them to wear down is dangerous.