Sensitive tooth after 3 weeks after filling

Hello, dentists of r/Dentistry/

I had a bigger cavity filled 3 weeks ago and my dentist didn't say anything about other treatments and just filled my upper molar.

Now, after 3 weeks it began to be sensitive and painful. Both hot and cold fell sensitive.

Do you think I'll have to get a root canal, or it's just the filling?

Thanks for all of your help here on reddit!