He probably was asking you the tough questions thinking he was making you seriously contemplate the reality of your situation. He wasn't very tactful, but as a physician, he probably sees many girls in similar situations and is probably worried about the trend. You're going to have to steel yourself for more comments and questions because they'll be coming as you show more. This is par for the course when you are pregnant as a young teen. I'm sorry it annoyed/hurt you, but this is just the beginning. He would do you and all his patients a disservice if he sugarcoated and made out like life will be peaches and cream for you. It's going to be hard and he wants you prepared. Again, he might have been nicer about it.
Ultrasounds are not good for the baby. Don't be in any hurry to have them. They normally don't do them until you are in the second trimester, which is why they can detect the gender of the baby. In the old days, if you got one at all, it was just that one unless there were problems.