too MANY or too FEW calories???? INSANITY day 30

Im currently in week 4 of insanity, just 2 days away from my halfway mark! But im starting to panic. I am an 18 year old girl that weighs 165 lbs and is 5'3". My first week of insanity, i dropped 5 lbs. I was really happy! But by the end of the 2nd week, i was back at 165. Now, in my 4th week, i am still at 165. I AM noticeably slimmer: ive lost over an inch from my waist, and my thighs lost the protruding fat part on the sides. Ive amped up my veggie and fruit intake, and decreased my grain and sugar intake by A LOT. Ive been eating healthy, all natural, organic meals and snacks, with very VERY few processed items. However, ive been at a calorie intake of about 1200 to 1400. Ive tried calculating this basal metabolic rate stuff, combined with my activity level yada yada, it doesnt make sense to me. Can someone please explain how it works, with my calories burned and all? How many calories should i be consuming? I live a rather sedentary lifestyle outside of insanity for 40 min. a day. I also weight train 3x a week. for an hour each time. How many calories should i be consuming? Ive researched stuff about plateauing, is that where im headed if i continue to eat low cal produce at only 1200 calories a day? I want to weigh 125 lbs, but im losing hope am i in starvation mode? I thought only fruits and veggies were good for me...? Please help