LJ you are not a bad mother, my precious girl
Do you call him by his name or do you have nicknames for him? DD knows her name but we call her that mostly, we have friends with a child the same age and they generally call her stuff like 'princess' and she doesnt respond specifically to her name. That said DD has some pretty serious selective hearing going on at the moment, so DS could be doing that! If W doesnt want to 'hear' his Mummy then he may very well be turning his ears off
Does he respond to noises and can he hear pinpoint where a noise is coming from? ie car out the front or back. He is definatley saying words that arent the normal 'non words' for want of a better term. DD didnt really start getting adventurous with words until about 18 months and its still often not understandable to others.
If you are super concerned in another few weeks, maybe see your Dr.