it's been 3 days and I just feel starving hungry all the time, even when I've just eaten. I'm drinking plenty of water, keeping exercising, but still, just hungry all the time.
I've been there. I've lost 70 lbs from my all-time high weight. When I started diet and exercise, I was also hungry all the time. I tracked everything on my Fitbit and would just feel enraged ("hangry," if you will) when it said I couldn't have any more calories.
I swapped to Keto, and while Keto is pretty hardcore, it definitely convinced me that the sensation of hunger is directly correlated with blood sugar.
So my advice is...
A) Stick with it
B) Try cutting out all carb-centric meals. No potatoes, pasta, rice, corn, bread, or sugar.