My 3 month old baby is refusing to eat

My son is 3 months old .. since day one he was never a big eater at about 1 1/2 - 2 months he would scream through his bottles fight me gag spit it out . I’ve taken him to his pediatrician and she wanted me to bring him in and feed him and requested me to go see a speech pathologist. I saw one who told me he just has really bad reflex . So I took it for what it was and did everything she told me to do and absolutely nothing has helped he wasn’t gaining enough weight so we put him on a high calorie diet . torwards the end of his two months he was eating great would take 3-4 oz with no problem now all of a sudden he refuses to eat all together he will only take 1-2.5 ounces . I can’t help but think my kid just does not want formula and my doctor won’t let me introduce baby food yet even though I think he is ready for a few bites with a bottle or just rice cereal in the morning . he never seems interested I have no clue what to do anymore. Any tips? Or anyone have a baby that went through this ? My mother said when I was a baby she had to put me on cows milk when I was 5 months old and would put liquid vitamins in it . I know obviously he’s way to young to try that but I will take any tips please !