wanting to help my 4 year old son

My almost 4 year old son has very big temper tantrums and the ones that concern my husband and I are the ones he has for no reason at all.  He doesn't care who's in the room it'll be a very big yell.  I accept temper tantrums at that age but I don't understand why he has so many for no reason.  Besides his fits, he's a very smart, happy, funny, social child, coordinated.  When he does have these outbursts, we have him stay in his room for a few minutes to cool down and it usually works.  We are very consistent when we dicipline and when we say "no" it's no.  We don't yell or hurt our child when they have a fit although we make sure we get eye contact and explain why he's getting a time out.  At times we take away privileges.  
Once he asked my to make him something to eat and I told him I would but he started yelling for the item he has already asked for and I agreed to make.  
He can be drawing a picture and I tell him how nice it is and how good he is at drawing and he can tell me "no" loudly.
I've read up on so many things on line but nothing seems to answer my questions.
He's starting school next year and I want to understand what "ticks" him off.  He has every reason to be happy all the time.  Most of the time I need to give him a hug to reassure him that we love him.
I have an appointment made with his doctor to discuss his behavior.  
If you can help me with advise or suggestions I would appreciate it.

[Kevin Kennedy, Ph.D.]

The behavior you describe does not sound alarming, certainly not anything that would suggest Asperger's or any other condition along the PDD spectrum. From your point of view, there does not appear to be a reason for the behavior, but it derives from some frustration that your son experiences (even if it is not obvious to you). Tantrums are a normal part of development as children learn to manage the strong rush of feelings that accompanies frustration.

[123rainbow]

I've been reading a lot on asperger disorder but I'm pretty sure it's not what he has...  He has great eye contact, very coordinated.  He's quiet shy but will  still be seen playing with friends.

[123rainbow]

Thank you Kevin!  I also think it's due to frustration although when he has a "fit" for no reason, I just don't understand why.  He is my 2nd child and I've not had to go through this with my first.  We're meeting with his doctor next week so I'm hopping he can suggest some good tips I can use to help him.  
The fact that I'm consistant and firm with his discipline is what make it hard to think I'm doing something wrong.  My son is very hard headed and stubborn!  Although he has way more positive things going for him than negative!

[Kevin Kennedy, Ph.D.]

The fact that he is having tantrums is not an indication that you are doing anything wrong. Tantrums at this age are not unusual - it comes with the territory, so to speak. If you want a gauge with which to compare your behavior management methods, read Lynn Clark's book SOS Help for Parents.

[123rainbow]

I will deffinetly read that book.  
We've had an amazing weekend with our son.  He was happy and communicated his feelings with us.  He played outside with his brother and friends and was just loving it!
Thanks again!