He is three years old - probably an inhibited disposition or perhaps just a shy and cautious. Relax - he's only three! Sounds very normal to me!
If your child isn't used to being away from you, then he may very well need more time to adjust to the daycare environment. Children come in all types of beautiful personalities, and it could simply be that he is shy.
Unless he is exhibiting unruly destructive behavior, I would suggest that it is much to early to worry about specific personality disorders, behavior defiant disorder, or even attention deficient disorder.
On the other hand, three years is about the right time to be seeing autistic behaviors in those children effected with developmental disorders on the autistic spectrum. I wouldn't worry however, unless he demonstrates difficulty with eye contact, and interactive play. If he seems disconnected even at home, then I would suggest seeking the opinion of a pediatrician.