A.A.
You may be right, that he has a problem. He may not, though. Second born children tend to develop language more slowly than the first born. Also, boys usually develop more slowly in that area. It's more important that he makes contiued progress than when he reaches different stages. A speech therapist will help you pinpoint the area he's struggling with. It's good to address it, but I don't think you need to stress about it too much.
I'm sure you've already found that reading to him, telling him what you're doing while you do it, and just talking around him alot wiil help.
My nephew, who turned three last May is also a little brother. For the longest time, he wouldn't use words. He did a lot of pointing and grunting and has just recently started speaking like other kids his age. This was around the time that his sister started kindergarten.
Your son could very well have a delay, but not really have a problem. It might just be his temperment. Some kids are just not too interested in speaking. Keep checking into it, but don't be worried, assume he's normal until you hear otherwise. I'm sure that in no time your problem will be getting him to be quiet! :o)