I don't know what to do next-Is this starvation mode now?

This is long...

Hi, I am now confused of what is the next step I should do. Last year, at the end of the year around November I guess, my weight went up to around 151-152 lb or so, a few pound of it and it'd be 1154-155lb-my usual weight last year was around 143lb, and I am 5"3 tall.

So I started losing weight and ate food by counting calories based from what MFP calculated it for me. Then 4 or 3 month ago, my weight didn't get any lower that much anymore from 116-117lb. I have looked around in the internet and it seems that it is because my weight is closed to the lowest range of my BMI chart and I am scared that I'd hit the plateau so I adjust my diet to eat around 800-900 kcal for a few days. Of course my weight dropped. However, then around those time I got scared that since I ate too little, my weight could gone up again and it could turn out worse-I could have weight more than my old weight last year.

So I continue to eat around 800-900kcal, mostly around 800kcal range. Some day within a week, there will be a day or 2 that I eat more around 900kcal-1000kcal. Now my weight is getting too low, currently I am 102.2lb.

I am trying to increase my calorie intake a bit, little by little. I have read that as long as I don't eat more than my TDEE range, my weight won't gone up, but it did. It is not much, just 2-3lb but to me.....it's discouraging and I am afraid that if I continue to eat more calories my weight could have bounce back to the same I was weight last year or worse. The community message board I went before this describe this starvation mode to be very scary outcome. I should join this community sooner, damn it.

So what should I do? If this is because starvation mode and how long will it last? Will my weight bounce back that fast and that much? My goal weight is104-105lb. I tried to eat up to 900kcal on last Monday and my weight stayed the same, so I tried again on Tuesday and my weight gone up 1lb.

Today I lower it to 841kcal instead. I did tried this at the beginning of the month before but my weight gone up a lot within 2-3 days, so I usually lower my calories intake to be within 800kcal range as usual. Am I over reacted and just being overly paranoid since I have read that sometimes it's also OK if our weight increase a few lb within a week, it will dropped a few days later? But then...how do I know it's because of startvation mode or just because of the food I eat (more carb/sweet/sodium than usual)?