I went through this with my Ryan, who will be four in September. He is my first child and I was beyond worried that he wasn't saying things. He didn't even really babble either. It was just, nothing.
My thoughts went crazy as to what could be wrong. Reasons ranged from the fact that he was a boy, the first child, a late bloomer, etc. I had tests done and even did speech therapy. My doc told he would talk when he was ready and he was right.
I was surprised at the things he said for the therapist that he did not say for me. Sometimes it takes someone else to bring it out. As long as he has not had many ear infections or any other health issues, I would say that it's probably too soon to start worrying. For us, Ryan didn't really start talking until he was closer to three.
I would see what your pediatrician says and maybe have a hearing test just to be sure.
And I agree with the "put the flash cards away!" advice. He is much too young to teach things too unless it is in a fun environment for him. When I approached Ryan's teacher about the things I could do at home for him (and he's almost four) she said not to push anything now. If we are playing and I want to explain things to him to make things interesting, I could do that, but their attention span just isn't up for that kind of stuff yet.