Toddler takes a few bites each meal

I'm seeing a feeding specialist before anyone says anything. They cost 380 per visit out of my pocket and my includes phone calls to ask quick questions. I just need some mom advice right now because I'm so stressed out.

My 3.5 yo used to be such a good eater and always ate a wide variety. He had an incident where he stopped eating and swallowing for almost a month. We had so many tests and a surgery for them to just tell me it was mental. We have been seeing a feeding specialist and he since improved before that but never back to the same. He now tells me he's hungry tells me what he wants then will take literally 3 bites and scream that he's done or mess with his plate for 40 mins and not eat at all. He's on the very low end of normal and I'm just so nervous that he isn't getting enough nutrients. His Dr just says keep trying and presenting and I'm doing everything they suggest but he is still so difficult to feed.

Does anyone else's toddler barely eat ? I feel like the worst mom in the world.