Cardio 45-60 minutes 5-6 days a week is perfectly normal and healthy. Are you strength training? If not, add that in.
Your eating level sounds reasonable. Combined with your weight and your exercise level, you should probably be losing about half a pound a week, which is perfect!
If you've lost that much weight that quickly, at your weight, I would suggest this probably more water weight than fat weight. It's very difficult for anyone of your size to lose 2lb/week of fat, and probably near impossible on 1700 intake calories and only 1900 a week burned. Those are very reasonable stats, not extreme diet levels. As I said, that comes out to about half a pound a week loss. Now, the maths doesn't always work out exact, but it's rarely 4x as much as calculated!
So what you do is ...
1. Set your fitness goal to be more accurate. It's fine to do as much fitness as you feel comfortable and safe doing, but never exceed your goal. If you want to do more - change the goal. You can do that on the fitness page. The goal is what is used to calculate your calorie intake needs, not the tracked exercise, so it needs to be accurate.
2. See how the next couple of weeks go. Three weeks isn't very long in weight-loss-world. If it's water weight it'll settle down and you'll start losing more realistically (or stabilise). If you continue to lose weight at this rate after a few more weeks, consider seeing a doctor to see if there is something going on with your body.
Deb, in New Zealand