Mommies, who is feeding him with formula? What do you give him? We're …

Mommies, who is feeding him with formula? What do you give him? We're 2.5 months old, a boy, he gained 600-700 grams in a month, weighs a bit more than 5 kg, Should we continue feeding him? Skinny My milk is probably liquid, but he doesn't cry otherwise I think Should I? All his peers are chubby, and mine is skinny straight up Will he refuse from the breast later?