Normally you would need your coolant flushed every 1-2 years. I'm not sure on the details why it was recommended to you to flush it twice last year. If you are loosing coolant and refilling frequently, it's important to make sure you have a 50/50 mixture of antifreeze and water for proper cooling of your engine.
There may be many reasons why your coolant has become contaminated and requires frequent flushing. That is best discussed with your technician who regularly services your car. Or seek out a local experienced technician who can best advise you.