I've been on a plateau since December. I was eating 1200-1300 calories a day, didn't lose a single thing. In fact, I gained, and then lost, then gain the same 2 pounds continuously.
I tried raising my calories to 1500 a little over a month ago (maintained), and then dropped down to 1300 under two weeks later. Did 1300 for a week and hated it. I was tired, hungry, obsessing over food and just in a rotten state. This whole state of yuckiness was amplified when it came around to getting period (sorry, this is a little TMI) last week, and it came, and then stopped. Then I realised that ever since I had been plateauing, my period had not be normal. it was late, light, went for 2 weeks, stopped and started for 2 weeks... Not normal, and not good.
So I did some research. Apparently, I have been eating under my BMR (basal metabolic rate,
http://www.bmi-calculator.net/bmr-calculator/) since August... by 200 calories, not including calories burnt through exercise (I never ate back my exercise calories).
So I bumped my calories up, and decided to eat back 75% of my exercise calories (I was eating at 1500 which was a deficit, and then if MFP said I burnt 400 calories, I ate 300-250 extra, so still netting around 1500).
I'm only a week (barely) into this, but my energy levels have improved, I'm not obsessing over food, my work outs are better, my period has started and continued (!) AND I'VE LOST A POUND... DURING TOM! That never has happened to me before.
Now, I know that the likelihood of this all being 100% connected is slim, but it's encouraging. I fully expect to see a slight gain in the scale tomorrow or next week, or at some point. I think you have to stick it out a month to see what the overall trend is. If it's down, I'll stick to it until it stops, if it's the same, I'll bump up another 100 to see what happens then, if it's up, I'll take this as a maintenance break and increase my deficit by a further 100 and see what happens.
I totally understand your fear of gaining weight. I've lost 30lbs by sticking to 1200-1300 calories. But that was when my body had more fat stored to dispose of. And really, I can't maintain for the rest of my life on 1200 calories. You do need to feed your body, especially when your exercising.
I hope some of that helped!