You are not a bad mother DD - you are a concerned mother!
Lilydust is right - some of his words aren't the common words so that is a good sign.
Does he respond to instructions? For example "go and bring me your shoes" That is an indicator of receptive language when they can understand and follow instructions.
As for how many words he says at the moment, DD doesn't have that many either, but I am seeing a paed for her reflux, asthma etc so she is being monitored pretty closely for all her development. I am waiting for that "word explosion" you hear about too!
If you have any concerns I would get him checked out by your GP and get a referral to a speechie or paediatrician, I'm an early childhood teacher and have taught kindergarten so I see kids who's language skills are behind and if they had had a little intervention before they came to school then things would be much easier for the child.

I am sure he is ok, but it is hard not to worry as a mother - trust me - I know!