I exercise 50-90 minutes a day, eat clean food, never exceed 1600 calories and I cannot stop gaining weight. (174 cm; 64 kg). It is slow, but constant?

Something amiss. Based on your age, gender, weight and height your basal metabolic rate is around 1400 cal/day: thats what you need just to live without moving at all! Odds are you burn more than 200 cal just moving about, without including your exercise. So either something awry with you metabolism and/or your estimated caloric intake. You should review this with your doc.
For clarification... Hello,Nathalie.Your current weight is normal and will protect you against many diseases including adult-onset diabetes.Your current BMI is 21(overweight BMI is 25 or higher, underweight BMI is less than 18.5).You are exactly where you should be for weight.It is also great that you exercise.The Mercilon may cause estrogen excess and this may cause increased body fat (that may be what concerns you).