I am worried about my 15 mnths old son...is this Autisum ?

My son is 15 months old...very active n playfull.He started to walk when he was 11 months old .He plays well with his toys...loves to play with cars....he pushes them arround.He knows when i call him name, or say NO to something and thats about it...I read books to him since he was 6 months old...still he has no preferrences nor does he recognise what i am doing for him...really does not care, i try to teach him parts of body like nose,mouth...he just thinks of it like a play...he does not repeate anything i say...nor does he follow any instructions...i am very very worried about his behaviour. He babbles a lot....more than 10 words easily...but none with a relevant meaning....he does not even call me mamma or his father dadda...he just says those words anytime he feels like telling.I am doing all i can to help him understand n respond but so far no success...i am very desperate n need help. Is this a sign for Autisum....please help