I don't feel weak, my BMR was 3800kcal, I used to eat around 2600-2800 kCal (not really counting calories). I'm currrently eating around 2200-2400 (my current BMR is 2100).

I'm eating a healthy mix of Protein, Carbs, Fiber, Vitamins (not "diet food", I just eat less) and I'm followed by a dietitian.