I lost about 100kg over the course of a year with extreme deficit AND extreme exercise. I did no reading and did all the wrong things. That was four years ago and since then I've managed to use my body as a little science experiment and try a few things out, read a lot and here is what I have found. I've existed for extended periods in the last three years between 9% and 20% BF.
For me it's always about body fat, that's what determines what I should do. I find that I only start having to worry about losing muscle mass once I get under about 12-15% BF, over that and I'm pretty much fine.
For sanity and physical well being I tend to take it easy every four weeks even when dieting hard. I will eat just below maintenance or at maintenance and back off exercise slightly. This isn't really important until I' quite lean, but it's more of a sanity and general energy thing when I'm not so lean.
If you've read stacks of articles then you know fat loss is diet and muscle building/maintenance is done in the gym. This is absolutely true for me. I've packed on the most muscle doing the Stripped Down Hypertrophy program for about three months and just changing exercises around every four weeks. Like anything I changed programs when gains petered off. Find a program and do it for six weeks or so, people smarter than you or I have made them and even if gains are mild it's six weeks of the rest of your life. You will learn about your body either way.
I would suggest you need to change things up, and you need to monitor your food intake. You give no idea of your body weight, but if you are actually taking in 1800-2100 calories then you need to prove this to yourself. Add measurements such as BF% and tape measurements to your arsenal so you know if some change is happening. I've had periods where scale change was minimal but tape measurements were noticeable.
I'd basically suggest after this length of dieting to take a week or two off eating 500 calories extra or something. Fat gain will be minimal in that period and it'll probably improve your mental, hormonal and physical state. Take that time to pick a program that's outside your comfort zone from the site, and a diet that works with your lifestyle and following them both for 4-6 weeks and see what happens. Reacess at the end of that.
Good luck, nice work on the 30kg.