Toddler won't talk but knows words.

My son turned 2 a couple of months ago and still won't talk unless he's prompted. We have a set of 150 flash cards and he can identify the picture and say it but he will only do it when he's asked. He only says Hi or Bye or Thank you when he's told to say it, and he never tries to speak on his own even when it's something he knows. He knows the names for his favorite snacks but when he wants something he cries and screams and just shakes his head if we offer something he doesn't want. We've tried refusing to give him anything until he says it, but he just screams until he's choking, so it doesn't work. I don't know what to do anymore, it seems like he's always crying about something. He's been evaluated for speech therapy already. 😥 I don't know what to do.