1600 – 1800 calories seem low for a male, but it would depend on your height. The data you entered was Female 56-year-old male 5’8″, 164 pounds, 7 hours of sleep, 10 hours very light and 7 hours light activity. Your healthy body weight range is: 139 to 169 pounds and you are within your healthy body weight.
Your calorie needs are determined by how many calories it takes to run your body (BMR = Basal Metabolic Rate) plus the calories you expend doing activities including structured exercise programs. My calculator is designed using formulas used in current nutrition practice and the only subjective data you enter is your activity hours. Do you think you over estimated how much activity you get?
Go back and re-enter your data, but this time leave your activity hours blank. Check the calories in Your Nutrition Facts. This amount is your BMR. Now click on your browser back button and add your activity hours. What is the difference between your BMR and BMR + activities?
The calorie amount in Your Nutrition Facts is a guide for how much to eat to maintain your weight or change your weight depending on the nutrition goal (loss or gain) that you entered on page 2 of my calculator.
Bottom line is if you eat more calories than you need, you gain weight and if you eat fewer calories, you lose weight. If you eat the right amount, you will maintain. I would recommend you ignore minor fluctuations in your weight (+ or – 3 pounds) which could reflect shifts in the amount of body water you have on board.