>My doctor said he doesn't know if it's common enough because they are not instructed to collect this information.

Some other countries are collecting this data, and it's not uncommon. Prospective studies (which compare cardiovascular health measurements of a cohort pre- and post-vaccine) show a myocarditis rate of around 0.1-1% in teenagers. https://pubmed.ncbi.nlm.nih.gov/36602621/ https://www.mdpi.com/2414-6366/7/8/196 . Compared to no observable increase in the rate of myocarditis from covid infection itself: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9025013/