I think you tell him exactly what you said here, that you are feeling sluggish and don't feel comfortable growing any more....and maybe add that you are happy you've been able to grow this much for him and that you don't regret that, it is just that you've reached your limit. He should be able to respect that.
Also agreed with the above posters, work on increasing your activity level steadily, and also work on improving the quality of what you eat (more vegetables and fibre, less junk food, etc).
Good luck!
14 years
