This use to happen to me. I would end up leaving with no answers, it was like he had 15 minutes with me and he had to move one.
So, I make a list of questions, one time I even had the doctor take the list from me and go through it one item at a time. And I got my answers.
You have to stand your ground, you pay for the visit, so don't let them push you through the system, just because they are only allowed so much time with each patient.
Or look for a new doctor.