Are you supposed to eat less on your non-active days to lose weight???

With exercising 3-5 times a week and strength training 3-4 times per week, I'm between lightly and moderately active, so I can maintain on 2100-2300 calories. I'm trying to lose weight, though, so I eat anywhere between 1700-1800 calories per day.

However, some days I can't work out (like today for instance- It's SOOO frusterating!) What do I eat on those days? Should I eat less than the 1700-1800 or what?

You should try to maintain a deficit but don't go below your BMR (the amount of calories your body needs to exist if you stayed in bed all day). You can calculate it here: http://www.bmi-calculator.net/bmr-calculator/

If you find it hard to eat less on the days you dont work out, try looking at your calorie intake over the week instead of day by day. I find it easier to focus on a weekly deficit. You said you can maintain on 2100-2300 calories, so multiplied by 7 that is 14,700-16,100 calories each week to maintain. If you want to lose a pound a week you need to subtract 3500 calories from that, so you should be eating between 11,200-12,600 calories a week.