My sons doctor said he isn't talking enough: Advice?

My son is 2.5 years old and just recently had a check-up. It went well, but His doctor said he should be speaking more and saying more 2-3 word “phrases or sentences.” He does say a few two-word sentences, numbers, colors, shapes, and a lot of other “single” words. We do work with him with flashcards, writing w/ crayons, learning shows on tv, etc. He knows what things are & what commands mean. We do not talk baby talk to him. And he does not go to daycare. He’s very vocal, yells, screams, shows every emotion, etc. Have any other parents out there gone through this with their son? Do you think boys are slower learners than girls, and he will start speaking more sentences in time? What is your guys’ advice? Thoughts? Thank you.