I've heard this anecdotally. Just found this study on the CDC website about it:

https://www.cdc.gov/mmwr/volumes/71/wr/mm7102e2.htm

"These data suggest an increased risk for diabetes among persons aged <18 years with COVID-19, which is supported by independent studies in adults (4–7). These findings underscore the importance of COVID-19 prevention among all age groups, including vaccination for all eligible children and adolescents, and chronic disease prevention and treatment."

I would trust your doctor. It seems difficult to be on top of these new findings in covid (and quite frankly people do NOT want to hear or talk about covid/long covid anymore-it's such a hot topic that is very triggering to some), so to have a doctor that is staying up to date on these studies is really important in my opinion.