Just looking for some reassurance

I have a 22 month old little boy who is going to see a pediatrician as the doctors ave concerns hes showing signs o Autism.

About him: he was such a happy hyper extremely social little boy. He would chat and wave at people when out and about. When at home he would be constantly on the go chatting to himself giggling playing with toys and interecting with who evers around. All this started to change around 18/19 months old, he no longer chatted to people when out he started sitting in his pram holding his ears and quiet. People we came into contact with on a regular basis started to ask if he was ok and say he doesn't seem like his normal self. He stopped being hyper at home and started sitting on his own spinning wheels on his cars. His cuddles have turned into him rubbing any skin thats not covered on you, rubbing his face on your feet and holding your ears. He has 2 brothers 11 year old who has asd but hes hyper very lound can be aggressive and a 9 month old. If his brothers go anywhere near him just even sit next to him and play with something else he gets so angry screams and pushes them away. He won't even allow me to sit and read him bedtime stories with him anymore he just wants to sit on his own with the book. Hes changed so much and feels like a different child sometimes. 

You would think i would be handling this alot better with being here before but this time feels far worse. My 11 year old is so much different he still had communication he still had his personality butt my 22 month old seems to be slowly losing his, we have 2 people that are seriously indeniel of whats going on my dad and my mil. My dad gets mad when people say about his speech saying hes only young hes doing well which he his hes doi g brilliantly but he was speaking so much better and much more often than he does now a few months ago even my mil said she can see speech regression now.

I feel so responsible like i am not trying hard enough with him, i feel it maybe because i don't spend as nuch time as i should do with having the 9 month old. I do try though i spend alot of time constantly repeating his name tapping his shoulder trying to get his attention it takes me ages just to get any reaction at all from him even touching him gets little response alot, when i do get his attention am looking to keep it for 10 seconds before i have to start again. I am not sure if hes just ignoring me though. Then theres the people who say if i look at a child with no issues its obvious he has issues, but with my eldest having asd and youngest only being 9 months old i really don't know and i really don't like comparing them. One of my biggest worries is am i over reacting for no reason as my eldest as asd.
If i was to go of my deep down feelings i feel somethings not quite right, its hard to explain with my 11 year old and 22 month old i have always had this odd feeling but i dont have this feeling with my 9 month old. Is it just me? Am i being paranoid? Am i just jot trying hard enough for him?

Sorry about the lengthy post.