A mom that doesn’t know what to do

Ladies that are mommies . PLEASE HELP ME 😩, my 4 month old drinks Similac soy (pink can) . She wasn’t gaining weight correctly like I told them so the doc took her up from 4 to 6oz every 3 hours , she was doing great & now she barely eats maybe 1-2oz & even getting to 4-5 oz is a battle of her turning her head , wanting to play or cries . I have tried baby girl on solids like oatmeal, bananas & apple sauce . But idk what to do I’m so afraid she’ll drop back down & become underweight & undernourished. Does anyone have any advice??