Girls, literally crying my soul out ? What can I give for improving ap…

Girls, literally crying my soul out ? What can I give for improving appetite of babies? He doesn't want to breastfeed at all. Earlier he demanded every 1.5 hours and now it's 3-4 hours then with difficulty takes breast. At 5 months old he weighed 8 kg, height 69 cm, and in 6 months he didn't gain even a gram or centimeter! ? Afraid that he won't become weak☹️ P.S. I was sick for 5 days and had a runny nose. Now much better