Feeling Down

I've been eating about 2000 calories a day for the last year, and I've lost more fat in that time than I ever did back when I was eating 1200 calories a day. My primary focus is strength training, and I'm smaller now than I've ever been before, even though I've weighed less before.

All that aside, it sounds to me like you may have a distorted view of your body. I know comparison doesn't always work, but you're three inches taller and fifteen pounds lighter than I am. Your profile picture shows a thin person. I'm not trying to push my standard of beauty or health on anyone because who am I to tell a complete stranger what's right for him or her. It just seems to me that I see some extreme behaviors and ideas in your post. Have you considered talking to someone about it? I don't necessarily mean a counselor. I'm thinking even about your doctor or a nutritionist, someone who can offer some insight into healthy weights and/or weight loss.

You won't gain muscle eating 750 calories. And as you're near the bottom of a healthy BMI and going by your picture, I wouldn't worry about losing weight at all.

The huge majority of people don't lose consistently every week. You will hit plateaus and minor gains because our bodies adapt quickly and so will fluctuate. While a gain is demotivating, it's just a small part of a much bigger picture. Eating 750 calories is not going to get you to reach your goal. Our bodies don't work that way, you will crash out rather than become healthy. You need nutrition to be healthy. You are starving.
Also, I'm not sure what you mean about muscle gain? By strength training you will not bulk unless you fuel yourself to bulk. Women who lift and eat at deficit (although not to deficit you're eating to!) usually see inch loss and become more toned. If you're focusing only on the scale number, you're missing half if the picture. At your height and weight, you are a healthy BMI and should cut yourself some slack. You look wonderful.