9lbs at 2month check up

My daughter was 7lbs & 3ounces at birth she lost that birth weight when we brought her home so we were feeding her every two hours & she gained her weight back plus a little more. I was told i didn’t have to do it every two hours anymore she gained her birth weight plus a few more she’ll tell you when she’s hungry which she does.. anyways today at her 2month check up the doctor was concerned because she dipped a little in her charts she said she’s not too bad off but she was in the 50 percentile and now she has a dip and only weighs 9lbs and a few ounces i don’t remember exactly. So she told me start feeding her 4ounces every 3-4 hours & come back in two weeks. I’m feeding her 3 ounces and she’s spitting it all up 🙁 idk what to do.. my boyfriend and i aren’t big people were both on the shorter side and my boyfriend is pretty scrawny 😂 I’m a little thicker but now I’m worried if she doesn’t gain this weight back.. what can i do? Should i be worried? Why did she dip like that? Is it because i was on a schedule with her and now I’m not? I feel like I’m over feeding her now