My 3 Year Old Has Declined In His Verbal Communication.

My 3 year old has declined in his verbal communication. He used to be able to talk with 2 syllable words and now just gunners a bit. When he is doing rhings by himself and not engaged by someone, he goes these rigid arm flapping and holds his breathe. We took him to his doctor and they tested him for autism and he wasn't even on the spectrum. They have ordered MRIs to see if they are seizures or some other neurological, movement or behavioral disorder. He also has anxiety and fears with certain things. He gets agitated easily and if something gets taken away when he isn't expecting it he has a meltdown and runs away to hide. We just don't know what to do or think. Our doctor put the MRI in as stat but the children's hospital can't get him in for 2.5 weeks. Just looking for advice and any assumptions to what this could be.