Our son was very delayed in a few areas. Speech and potty training. He was also having significant anger issues.
We took him to a therapist and he was diagnosed as borderline autistic. Of course we were totally upset by this. We never went back to this woman.
Our son is now 14. I'd say he is very different from other kids, and very special. He started out with drawing before he talked. We got him a standup chalkboard, and at 4, he filled it with O I O I O I and variations of those symbols.
He was obsessed with sprinklers. He'd watch them for hours. He drew them in perfect detail. He didn't want us to buy our present house because it didn't have them. This went on for 4 years. Then he was obsessed with public transportation. This also led to perfect drawing of trains, in perspective (at 7 years old).
He was a loner for many years, and we worried. Even when we had play dates, he would ignore the other kid to go play with the sprinklers. But he was very happy.
Now he is popular, and has varied interests. He is a straight A student. He was always loving, and energetic. He so wants a girlfriend right now...yikes.
I think that each person is so unique. As parents we worry so much about everything. But in the end, they usually turn out just fine. Just variations of what society views as "Normal".
I'm telling you, don't fret. Go with it. Be enthusiastic about everything that makes him happy. Its the best message you can give your child....."you are OK with me".