Calories/exercise/weight loss/working nights... ???

MFP set my daily calorie goal to be 1200. I am 45, weigh 156, goal weight is 135. My biggest challenge is that I also work nights as an RN, which throws my metabolism and exercise abilities off. I NEVER lose when I am on a 2 or 3 day stretch of working nights... I plateau, or gain, even though I strive to sleep 6 - 7 hrs/day. If I am off for 2-3 days, I start to drop... but then a night or two on, and bam - I might end up back where I started.

I just began incorporating weights into my workouts, so I know I am building muscle, which will more effectively burn fat. But what should I expect the timing to be on this? I was losing rather consistently on just cardio (45 min eliptical, 10 min running - unable to run much more d/t joint issues, used to LOVE running.... :/ ) but now that I have added weights in, I seem to have plateaued.

I keep my calories right at about 1200 on non-excercising days, and on the days I do get to the gym (I strive for 4 days/week, sometimes 5) I eat back SOME of the calories, but not all. (I gain, actually, when I eat back the calories, that's how sad my metabolic rate is)

Any advice on how to juggle this? I don't want to eat too little, as it's not healthy, and will drop my metabolism... but if I eat back the calories at ALL, I gain - so I try not to, but am then starving.

I feel like I am on a very tightly controlled seesaw, never sure if I should be eating more, eating less.... exercising more, less... hitting the weights or not.... there does not seem to be any consistent combination that works.

Thanks for any advice!