Still under assessment (toddler)

I have a beautiful 3 year old son with disabilities I first noticed that he wasn't developing the normal physical milestone stages at one years old since then I have been receiving a variety of support from portage, pediatric, physiotherapy and speech & language. However the support has been more let's get him to do this and that as we actually have no clue what we are dealing with! 

He was originally under assessment for Autism however as he has developed more he shows no sign of Autism so back to the start with an assessment the thing is they aren't looking at other possibilities of what it could be they don't give help or advice on the things you actually ask. As a mother of one I'm struggling to understand the lack of concern they have for him. He can say around 3 words but can't string a basic sentence together. He has a high intellectual rate and understanding he also has clear muscle waste on his legs and is unable to walk his behaviour is mostly happy (easy exited and smiley) but he hardly sleeps like hyper behaviour despite been fed a proper diet with no sugar rubbish. He can be challenging and is very demanding. I'm at my wits end I just want him to receive the help needed to actually progress him rather than feeling like he's just a lab rat trial and error.

Mentally speaking I'm struggling because to be honest I just don't know how to proceed with this for example he's desperately trying to be potty trained on his terms too but I can't find a potty suitable for him to use  it's sad to see my son has potential to progress yet is being failed by the system that is supposed to support him. If I could afford to go privet with his care I would but I can't how can I get them to listen and help me support him.