Back years ago when I lost weight, I would lose 3-5 lbs and stay that way for a while and then lose another 3-5 lbs. I ended up losing around 30 lbs over the course of 2 years. From 165 to 132. How long has it been since you last lost any?
Would there be a way for you to have a day with a few more calories without having blood sugar issues? You may have come to a point to where you body needs a little tricking. Your body is probably used to running on 1100-1300 calories a day and has down regulated to that.
It's great that you have alot of energy and you said thyroid was normal. Most doctors only look at TSH. Free T3 and Free T4 are what needs to be looked at to determine if there is a thyroid problem. As long as you aren't shedding lots of hair, no fatigue, cold hands and feet, then you can count out thyroid.