K.S.
My son only had 2-3 words at 18 months. At 21 months his language exploded and by 22 months he was speaking full sentences. Many boys speak later than their female counterparts. Unless you think he is having trouble hearing or has some actual physical issues holding him back from making sounds I wouldn't worry for at least a few more months. In terms of helping him: spend lots of time narrating what you are doing, naming things you give him, and read to him more than 15 minutes every day. Also teach him sign language for some basic words (milk, hungry, more, please, thank you, all done, and any others you think he would use a lot) if you haven't already.