Just to add a little more confusion to the discussion:

Our young man is 18, almost 19. I believe that it is developmentally normal to gain weight at this age. It's really the last "symptom" of puberty, and it's well enough known to have a common name--"freshman fifteen"--so called because college students often gain about 15 pounds in their freshman year. This is naturally a more difficult time of life to lose weight because you are bucking your hormones, but it can be done. Just stick with the diet prescribed by your doctor. It sounds like he put some real thought into it, and he seems to know you pretty well. Also, I know from my own experience that you are right that many of us should not weigh in more than once a week.