My son also has had issues with constipation from time to time, though it does seem much less frequent recently. He sometimes ignores me and can get very absorbed with a toy, but other times does respond well to me. He loves mirrors and can stack some of his toys well. He is usually quite happy all the time. Everyone does comment on how good he is, but many people do also comment on his slow development. He naps a bit much sometimes to I think. I'm really not sure what else might be pertinent information. Please, any advice or guesses would be nice too. Even if it is just to say I'm over reacting.
My first thoughts are that it would put your mind at ease to get him checked out so do that frist, Is he getting enough stimulation, are you the main care giver, does he go to day care, Is he shuffling around on his tush and crawling, you say he doesnt walk so what does he do with his body ..Is he eating well, do you play games with him, take him to parks to see other children , what would be his routine..