my son is like that..he's 2 1/2. he is only now really saying words and opening his mouth. that said, he does know a lot of words and does say quite a few.
things my HV said to me when ds was 2 and suggested to me:
talking to my son in simple terms (no over the top explanations of things) all the time you can, while out, at home. make sure that some of that time, my son is looking at me and my mouth move.
reading while my son is looking at me, bringing attention to my mouth talking and moving.
singing while doing the same
socialise him with other toddlers (mom/toddler groups, preschool, nursery, anything really)
have you talked to your GP or HV about this? they may have you see a speech therapist (we did this 2 weeks ago and the therapist said since out son is coming along with speech now, strings 3 and 4 words sometimes, and understands 2 and 3 step commands; there isnt much we should worry about now.) and to point things out to him instead of always saying whats this, whats that called.
it may be hard, but try not to worry unless you feel other areas of your son's developement are behind as well. just keep trying, and talking talking talking to him.
i know, its frustrating as hell. but he'll get there