Have just seen your other thread and realised you are at the start of this whole journey...
Regarding sensory processing disorder a good website is here. I particularly liked the 'symptoms checklist' - not all of them described my son but some were very familiar, particularly the tactile, auditory and internal regulation ones.
There's also a good book by Carol Stock Cranowitz called 'The Out of Sync Child' which can help you to understand what is going on a little bit more. If you don't want to buy a copy, try ordering one at your local library - it might help some other parents too. Strangely I felt this book wasn't as good at describing my son as the website above, but I do like her other book 'The Out of Sync Child Has Fun'. This book gives you ideas for how to meet their need for sensory input (if sensory-seeking) or get them used to more input (if avoiding) or just to regulate their sensory processing better.
I also agree with people on the other thread that it's worth going to your GP and talking about the way your child behaves that is different to what you would expect from most children of that age. (Sometimes we talk about NT children which stands for 'neurologically typical'.) You don't need to dwell on any problems with the school but if you have a list of things like 'he always licks the poles on the bus' or 'he screams really loudly to block out other sounds' or 'he keeps saying I'm hurting him when I try to brush his teeth' (all examples from ds2) they should get the picture. And it's a community paediatrician who will be able to do a proper assessment and say (in their opinion) whether they think your child is on the spectrum, or has other associated or similar disorders. Be warned, however, we didn't find the paed particularly helpful - it was only once we went to the occupational therapist (OT) that I really felt we'd found someone who understood not only why ds2 behaved that way but what we could do to help him (and us).
There's loads of discussion about sensory processing disorder on mumsnet: try this thread for a starter or just do an advanced search within the special needs topic.
hope that helps