Girls, hello. My daughter is 2 months old today. We had an appointment…

Girls, hello. My daughter is 2 months old today. We had an appointment with the pediatrician, and her weight barely increased, maximum 200 grams. What should I do? Maybe something's wrong with my milk? I feed on demand. She wakes up for feeding 1-2 times at night. The milk doesn't flow like in the first month anymore, maybe it's not enough? In the first month, she gained 1 kg, but now only 200 grams. Tried giving her formula, she throws it up. How can I increase lactation?