Doc said I’m producing too much?

Baby is 3 weeks. I only pump once a day just before bed. Baby eats every 2 hours. Occasional spit ups. But last 2 days baby has been fussy, straining to poop with nothing coming out.

She said baby’s belly is distended because he’s too full because he’s eating too much and I need to pump more to see how much I’m producing(which I know is wrong) and I over produced last child, I’m not trying to start that again...

She said to give him a half ounce of water between feedings to see if it helps him poop. Which I don’t think is right either.

I thought breastfed babies didn’t over eat....

Suggestions, help, tips to get this baby pooping comfortably- lmk! Thanks!