I'm starting to eat more to increase my lifts, but my parents (I'm 18 and go to college) are forcing me to go to a doctors appointment so that the doctor can tell us that I am unhealthy and give them justification to stop me from eating so much.

The problem is that I'm not even big! I'm 6'2 and 215 pounds, naturally skinny/thin-boned (I started at 165lbs) though 210x5 lbs bench, 330x5 lbs squat, 320x5lbs deadlift, 145x5lbs overhead press.
When I was 17 and 5 lbs lighter I went to my pediatrician who knew nothing about lifting weights and she told my parents that I was already overweight. Now that I am eating even more to increase lifts they are seriously concerned and I need to find someone to tell them that there is nothing to worry about since they won't listen to me.