You made a really good decision trying to lose weight before conceiving. Not only will it increase your chances of getting pregnant, but women who start pregnancy at a healthy weight are giving themselves far better odds for an easy and uneventful pregnancy and birth. If you do get pregnant before you're at your target weight, it would probably be wise to ask your doctor for ideas on how to keep yourself active and eating well.
I think 1800 calories a day is a bit higher than what you should be consuming if you're not exercising that day. One of the hardest parts about losing weight is finding the right balance of exercise and diet, so that you're not overconsuming and you're also not starving yourself. Your basal metabolic rate at 5'8", 210, and 29 years old is 1752 calories. That's how many your body burns in a day with no exercise (based on the average person's metabolism). 1500 calories may be a good target intake for you on days you don't exercise, at that rate you would see an average loss of about 2lbs a week.
I hate to say it but I would also suggest more cardio. 20 minutes, three days a week is not much. It isn't nothing, though - this may be a good place for you to start and get yourself into a routine, but eventually you're going to want to do 30 minutes a day 5 days a week in order to see results that mirror your diet changes. I understand this is a pain in the butt but serious weight loss is a real challenge. You can definitely do it. Even if you start with small changes, it's how big your COMMITMENT is that will determine your success. And you have some good reasons to make that commitment to yourself right now!
Good luck on everything!! We'll be here for you :)
