The child is not eating well, either they have too much milk. What sho…

The child is not eating well, either they have too much milk. What should I do? I sit before bed and breastfeed, but it's so hard! The baby eats little, but she's gaining weight. I don't know why this is happening. With my son, I hardly ever pumped. For two weeks now, I've noticed that there's too much milk and it stays even if I feed her twice with one breast. Can you advise what to do? And which electric breast pump should I buy because I'm already tired from doing it by hand. I want to quickly express and go to sleep.