weight not coming off--hormone problems?

Hi guys, I've been on a very strict diet of 1200 calories and sometimes less than 1000, and have been exercising at least 3 times a week (rigorous running) for about 1 month now. I have only been able to lose 2.5 pounds in this whole month.... according to the calculator at myfitnesspal, I should've lost 3 pounds in a week, not 1 month! My roommate who was eating exactly the same thing as me, meal by meal, lost 10 pounds (she started at a much lower weight).
I have a history of messed up hormone problems. In high school I was diagnosed with PCOS and my testosterone was through the roof. I have had that corrected already, so I don't think that is the problem. What do you guys think is the problem? Why can't I lose the weight even with restricted intake and exercise???? I get tired really easily and cold easily too. Is it a thyroid problem?

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