My 8 yo son has gained approx 20 lbs in 6-8 weeks time. he is not eating any thing or any more different than he was. his activity level is also the same. yes it has decreased due to covid but the same as before the 6-8 week period. what could cause?

Doctor can examine: If a child is not sick and retaining water, then weight gain is likely to be due to eating more calories than needed for normal activities. His doctor can help decide what's more likely. If one eats 1000 extra calories a day for 2 months, he can gain 20 pounds. For example, an extra 12 oz orange juice, 12 oz milk, 1 slice of apple pie, and 1.5 scoops of ice cream in one day is 1000 extra calories.