The only thing I think of, like another mentioned, is if JC is lower carb, and now you are eating higher carb, it could easily be tons of water weight. That would be typical of coming off of low carb. BUT I'm unsure of the carb level of JC.

The only thing I would suggest would be to keep at it, and consider WW if you think the structure might help you.

The lose it website forum has a BMR thread going. I think that is the site the OP is referring to. The lose it ap is like my fitness pal in that you set a weight loss goal for the week but it does not tell you what your BMR is or tell you if you are going too low in caleries. ( for example if you are 120 pounds and six foot trying to lose 3 pounds a week or if you are 350 pounds trying to live off of 1200 caleries a day....there is no built in system and the BMR thread is suppose to help people have a general idea on where they should be.)
BMR is just a guide, but it is not a set in stone number. The Lose It app is wonderful and has help me with my weight loss but it is a tool. OP, Check the nutrient info in your daily info and make sure your protein is high enough 25-30% is best. I think you may be experiencing some water weight gain......good luck to you....keep at it....much of weight loss is trial and error and a commitment to never quit.

Exactly. See my sig? Exactly...

Also - why you're at it - you need a new doctor. If your doctor actually said the words "starvation mode" (which I find hard to believe) they need to be replaced.

As to the problem at hand - I have a difficult time believing it is true. No offense to the OP but I would assume you're not being honest and/or accurate with your caloric intake. At 5'9" you're simply going to have a hard time getting fat on 1200 or 1500 calories a day.

If you're being completely honest and accurate than you need to get a full work up by a competent doctor and not one that thinks you can gain fat due to "starvation mode".