No food

My 18mo won’t eat anything. Eats well at nursery but won’t for me or my husband. What do I do? When should I be concerned? We’ve done a mixture of sitting elsewhere, baby led and spoon feed, different food and textures. He’s only interested in sweet stuff so we’ve stopped that. Then he’ll only eat some cheese 😩 maybe a cracker if I’m lucky. What else do I do!? When do I get doctors involved because I’m so concerned about the lack of food. He’ll eat most fruits and all sweet stuff. Just no meals 🫠