Why have I stopped losing weight?

Ok, so I'm 18 years old and I'm 4ft 11in...
The problem that has recently occurred is that I have stopped losing my weight. I have been exercising for about 2 months... Starting march 29th! The routine I would do would be everyday do a certain amount of minutes of exercise for each exercise. An every weak I would either add another exercise to my routine or add another minute for all the exercises I was doing! That's plus a minute for every exercise. Well I got up to about 12 exercises an doing each for 7 minutes. And then I started staying at the same weight. I want to get down to 120... And right now I'm at 150. We started changing around the routine.... And doing it faster (no breaks) in an hour! And are still at 150 right now. But started that routine 1 week ago.... And are starting to wonder if it's a week before your period?.... That, that could stop you from losing? ... If the water that builds up for your period could be losing with what your exercising off?... But your not losing below what your weight is staying at yet. Bc of your period.
I would really like to know because I'm getting discouraged :( I eat below 2000 calories a day an am getting worried ... Help