It usually takes them a little while to "find their voice." As long as all other factors are good, I don't think you should be concerned.
I didn't get Mandie until she was 4 1/2 months old so she had plenty of personality when I met her. I think they are pretty much born with personality, though. Sounds like Bentley sure has one. You said he looked at you funny AND he yipped to let you know he had to go potty - sounds like a boy who knows what he wants
