Kid has not gained weight in a year

My kid is now 3.5 years old and weighs 33 lbs. he has hovered at this weight (plus or minus 0.5 lbs) for OVER A YEAR. He has grown well in height but nothing in weight. Like many toddlers, he is picky. But unlike many toddlers, he just isn’t hungry. I’d be delighted if he ate a high volume of anything. I’m truly on the brink of a nervous breakdown. Here’s what we’ve already tried:

• saw two ped GI docs and several dieticians. They independently recommend trying Periactin to stimulate appetite.
• Periactin on and off for 6 months. It seemed to help at first and now doesn’t seem to work.
• Kid shakes. He refuses Pediasure and most brands/flavors. We have had some small success with chocolate Orgain.
• safe foods. Very short list and even that takes a lot of effort.
• adding fat to whatever he eats. The only thing that works is butter in pasta.
• feeding therapy. Helped with texture exposure but otherwise unhelpful.
• low pressure techniques. He isn’t hungry.
• high pressure techniques. Sometimes works.
• eating with him. No difference.
• montessori kid table. He will sometimes eat but mostly tries to run away and play.

His daycare teachers say he eats at school but I don’t really believe them. I often find errors in their logs. His general blood work a few months ago was fine. He poops every day. Developing well in general though we did have to work through a speech delay.

I see so many posts saying kids “live on air and goldfish crackers”. Are you kids gaining weight? I’m losing my mind here.