Why would i have jaw stiffnes and pain weeks after i had a novocain (procaine) shot during at my dentist?

Many reasons: Depending on the injection that was used, the needle may have passed through multiple muscles and you might be having a muscle spasm. You might have kep your mouth open for a long period of time and the muscles might be angry from that. You might have an issue with the filling and not be aware of it. I would call your dentist and have them see you as soon as you can get it in.

Shot location?: Could be where the shot was, if it made the muscle sore, or if you had your mouth open too long and made it sore.

Possible Hematoma: Soreness could be due to a hematoma, a common side affect of local anasthetic administration. It is like a bruise and usually gets better with time. If not better within several weeks, go back or get 2nd opinion.