xad you're not eating enough
I eat enough I average around 1500 - 1800 kcal a day now which is healthy + I exercise plenty
At your height and weight, an estimate of your bmr is 2010 kcal, and exercising on top of that means you burn even more.
Your bmi is currently in the healthy range, so unless you wanna keep losing weight I suggest you start eating more again. bmi, however, is also a pretty inaccurate measurement system as it doesn't take into account personalised bone density/muscle mass/etc. If you really wanna know what's up with your body I suggest measuring your body fat percentage, you can get calipers online super cheap and that's at least more accurate than bmi, even if it's also not perfect.
plus, if you're under eating you're going to be losing muscle mass, just something to consider.