OK - your current Body Mass Index is 26.1, which places you slightly into the "Overweight" category (note: Body Mass Index is simply a ratio of weight to height, and NOT the same thing as body fat percentage).

You are currently in the 72nd weight percentile when compared to US averages (in other words, 72 percent of 169.5 cm tall, 19 year old US males weigh less than 75.2 kg).

The "Harris-Bendict" formula for estimating metabolic requirements says that if you are:

1) Sedentary (little or no exercise), you need 2177 calories per day.
2) Lightly Active (light exercise/sports 1-3 days per week), you need 2495 calories per day.
3) Moderately Active (exercise/sports 3-5 days per week), you need 2813 calories per day.

Of course, these are just estimates, but this formula has been in use for quite some time now because it's proven reasonably accurate for most people.

Based on this, it sounds like you're trying to lose weight far too quickly. If you exercise regularly, and eat around 2000 calories per day, you should see a steady rate of weight loss. But please note that weight loss is rarely linear - there will always be plateaus where you're stuck, and times (like around the holidays) when your weight goes up for a few weeks.

The fact that you are "panicking" about it may indicate an eating or anxiety disorder...please ask your doctor about this.

70 kilos would be a good target weight for you. But, at your age, and if you are interested in cycling performance, you could aim lower and still be in the "healthy" weight range. 66 kilos would give you a BMI of 23.0, and you would feel much stronger when climbing on the bike.

Best of luck!