5 year old boy behind socially

I have a very loving 5 year old boy. He has always been a bit behind, and seems to catch up eventually for the most part. We had him screened for Autism, and they said he had a few of the symptoms but not enough for them to say it was autism. We thought maybe he is immature for his age, so we kept him in preschool one more year. He is going to start kindergarten late august, and here i am worried again. He just seems different. He is always humming ( though its only when he is happy or eating).  He seems like he is in his own world. He does have a few friends that he plays with, but sometimes he does or says inappropriate things, and it seems like he doesnt know any better.  He is always interupting conversations, and repeats things alot.  I am not sure where to go from here. I worry that he needs to be protected, he is very sensitve, and his communication skills arent that great. I know what he is trying to say, but other people would not.  There are days where i think he will be fine, then something happens where he loses it and throws a huge tantrum because his socks are the wrong way or his balloon popped and he cant handle it.  I dont know if this is normal, add (my husband has it) or does he have a learning disability?

[Sally44]

The issues you mention do sound like they are on the spectrum.
When he was assessed who assessed him?  What area of the diagnostic criteria did he fail on.  You have mentioned he has communication problems, social interaction difficulties, throws tantrums at unexpected outcomes, has sensory issues.  He sounds on the spectrum to me.
He may be high functioning autistic.  That is the diagnosis my son has.  He too is different, but there are days when you question his diagnosis, then other days when nothing goes right.
If he wasn't assessed by a multi disciplinary team of professionals that have experience in diagnosing autism, I would go back and ask your doctor to refer you.  
My son also likes to play, but he doesn't always know how to initiate it or sustain it.  He is in a mainstream school that has experience and expertise in autism and aspergers.  There are around 5 children in each class who are on the spectrum.  This school has playtime and dinnertime supports and clubs.  They have a Social Skills club as well as mentoring and circle of friends.  
The difficulties your child has will be life long.  But he can be taught better ways to cope and interact.  But he will need to be taught it and he will have to mentally think it through rather than it coming naturally without effort.
If you can understand him, but others cannot, he needs to be assessed by a Speech and Language Therapist who has experience of autistic spectrum disorders and speech disorders.  She should assess his expressive and receptive speech, assess for Semantic Pragmatic Speech Disorder, auditory memory and working memory, Auditory Processing Disorder etc - google all these to see which seem relevant to you.  Problems with speech are bound to affect social interaction.  The SALT is also the professional who assesses for behaviour and social interaction skills.  She should put together a programme of therapy, social skills club, playtime/dinnertime support strategies etc.
The socks and balloon thing is probably down to Sensory Integration Disorder - google that to see if it sounds relevant.  Those on the spectrum typically have problems with sensory issues.  Their sensory perception varies day to day and throughout the day.  So they can appear deaf when you call their name, then respond immediately another time.  They may cover their ears at a sudden noise or throw a tantrum, then later on enjoy making a noise or going to something like drum club.  Any or all of the senses of sight, sound, touch, smell, taste, balance and co-ordination can be affected.  If you think sensory issues play a part I would recommend you google the name Olga Bogdashina and read an article by her printed in Autism Today.  In her book Sensory and Perceptual Differences in Autism and Aspergers, there is a caregivers questionnaire which you can complete to get a sensory profile of  your child.  The Autism Outreach Department in our city uses this questionaire so I know it is reputable.  An Occupational Therapist is the person who would assess for this.  His always humming is probably a sensory thing.  He might use it to try to screen out other auditory background noise.  It might be worth looking at Auditory Processing Disorder as that sometimes is present as well and he may not be able to habituate to background noise.  
You say he repeats things alot.  Do you mean things from TV or films he has seen?  If so google Delayed Echolalia and Autism.  Echolalia is typical in autistic spectrum disorders and it shows a different way of learning language and usually a different learning style.
I, like you, was concerned about my son starting school.  After attempting to work with his school with limited success, I eventually moved him to his current school.  I think you know that he will struggle and doesn't have the language or social skills to be able to cope.