It sounds like autism. I have a 7yr old who was diagnosed with autism. It is a difficult thing to come to grips with. A lot of people have a lot to say about certain behaviors and treatment and i am no doctor, just a mom who knows what works for her babe. It sounds like your son is falling into the spectrum, but that dosent mean that he cant grow and function as an adult. As far as the crawling. put on some music and crawl on the floor, do a dance with it and make it fun, do it everyday, autistic or not he is goig to want to join mommy. Be sure to get him a hearig test, he might have a hearing problem. Dont put any shoes on him that are not supporting his feet, hard, balanced shoes only. That will help with the standing. Play standing games with him hold his hands and guide him. Its good that you are getting him therapy, I hae done this as well. My son spoke until he was almost 1, then he went mute for 3 years. If he is autistic, and I think that he is, continue therapy but work with him constantly everyday thats the only way hell learn, even if it seems that its not working dont stop. I taught my son how to speak, express his feelings, read, write, letters, sounds, colors, shapes, numbers, typing, he even has a little sense of humor now :) I hope that your son is o.k, but if he is on the spectrum, some thing he will only learn from mommy, like how to tell knock knock jokes and how to bake a cake :)
It sounds like you have had some kind of an evaluation done in order for him to be in physical therapy and occupational therapy as well as speech? Was this ordered by your pediatrician? Does your child interact with you? Make eye contact? Is he upset when you try to cuddle him or pick him up? He should be sitting up and babbling by now at the very least. I would keep a log of your concerns and try to make note of the behaviors I mentioned above so when you take him to the neurologist you will have an idea of what he does and doesnt do as far as interaction. Is he a picky eater or do you notice certain clothing bothers him and is he a stickler for routine, these kinds of things, does he have abnormal tantrums or get upset in crowds. Note anything you may notice and log what age he met certain milestones. Gee I sure hope you get answers, unfortunately at this age it could be just about anything or nothing except he is a little slow. Hope this helps some.