What Can I Do To Help My Newborn Regain Weight After Losing Some Due To My Illness And Reduced Milk Supply?

My baby is now 5 months and 21 days old at birth his weight was 4 kgs he was 2 and half month old when i fall ill due to gallbladder attack and acute pancreatitis i was on iv drips for a whole month and my baby was exclusively breast feeding i tried to give him formula but it didn’t suit him he started to vomit. I was totally on iv trips so my milk supply got decreased before I realised, it was too late and he already lost his weight i was ill for 2 month then my gallbladder was removed after that i started eating and i am exclusively feeding him now milk supply is back but his weight is low. Now his weight is 6.7kg height is 67cm and head circumference is 42.5cm what should i do so that my baby get his weight back.