Newborn weight concern

My baby is born at 36 weeks at 5.8 pounds. He was 41st percentile at his first month visit and he got Covid when he was 9 weeks old. His weight gradually decreased from 10 to 9 pound in three days. We went for a follow up check and found his weight is reduced . But at that time doctor did not warn about me on anything even I asked . She said all good .

Then again exactly after 6 days today he had got His shots and doctor said he is 17th percentile and he did not get his nutrients properly . And asked me to add on formulae . So today he is at 11 th week . And weighs 9.15 pounds . Is this underweight and should I supplement ? According to me doctor did consider the drop during Covid and he is again starting to put on weight .