18 month old not speaking, strange movements

I'm curious about my childs development. Mikey is my son, and he's always been very social and happy all the time. No sleeping or eating problems since birth. He's always been a little slow to develop in nearly every catagory, but I'm starting to get a tiny bit concerned. He started walking at about 15 months, started crawling at about 11 or 12 so he's a slow and cautious baby. He only says a few words at this point; hi and hello, counts two three four, nana (mommy) and dadda. Occasionally says dog, juice and good. He vocalizes while eating, if he likes something he hums "mmmm mmmm". He seems to be reluctant to speak when prompted. I try to get him to repeat words and he smiles and hides his face, almost like he's shy???  He has started dancing with some weird dance moves, hands out to the side bobbing up and down. If I take notice and encourage him to dance, he does the same thing! Runs off smiling like he's shy. Lots of eye contact, responds to "no!" and when I ask "where's your juice?" He goes to find it.  

Just a couple weird habits, he shakes his head back and forth sometimes. He also screams a LOT and babbles nonsense words quite often. I just need to know if I should be concerned because I have to plans to take him to the doctor about any of this yet.

[jklaport]

I wouldn't be concerned but taking him to see his pediatrician won't hurt. All kids are different. He sounds like a really sweet boy.