Vegans

a doctor i spoke with told me to eat the majority of my calories in the morning and early afternoon; he suggested 600 for bkfst, 400 for lunch and 200 for dinner. He also said avoid flour and artificial sweeteners, and to get strength training in regularly. I started Sunday after having a bit of an off-plan early morning snack of leftover cornbread and 13 potato chips (255+150 calories or 405 total calories), and lost .2 lbs for a total of 1400 calories on Sunday. Then yesterday I tried all of this with no flour whatsoever, but with about 400 calories each meal for a total daily intake of 1217 calories with the exception of avoiding the artificial sweeteners and actually gained 2.6 lbs. I'm not sure that it's the artificial sweeteners because I still lost Sunday a little bit but had had some artificial sweetener in my coffee that morning. Does anyone know any pointers other than the elimination of starches that could be derailing my progress? any other helpful diet tips? I've also previously tried a low carb (3 g carbs) 90 calorie shake for breakfast with a 300 calorie lunch and a 200 calorie dinner, for less than 900 calorie intake that day or two, and did not lose but the doctor said do not eat under 1200 each day.