Loosing weight with pcos?

ok so just before getting pregnant with my third baby i was told i had pcos (i struggled to get pregnant with my first child and third) and this would probably be contributing to my struggle to loose weight. before having kids i never struggled to loose weight i was 10 n half stone and a size 10, but now im nearly 17 st and a size 20. ive had 3 big kids, 2 were 10lb 12oz and the other was 9lb 9oz. since having my 3rd i have at the gym every other day (at least 4 days a week) from 6 weeks after giving birth and have been swimming 3 times a week since then too, i have also been trying to limit my calorie intake to between 1200 to 1800 and 6 days out of 7 i will keep to that i usually have about 1800 to 2200 on the 1 day a week. after having my 3rd i was just under 15 stone and a size 16 and that was before my uterus went down. it makes me feel so down that im puttin in all this effort to lose weight and all i have done is gain 2 stone a 2 dress sizes and i havent been to the gym the past week coz i just feel like giving up. before i was told i had pcos i was also given orlistat to help with the aid of weight loss and that didnt work either. i was also tested for a thyroid problem but everything came back fine. i have no idea how to lose this weight as all my efforts seemed to have not worked has n e 1 else with pcos gone through the same thing and found a way that has succeeded, or does n e 1 else have n e advice, i am currently on a waiting list for an appointment to see my doctor as they do appointments once a week and they r all full up and the only other times they have is an open surgery between 4.30 an 6pm on a daily basis but my husband works that time n has the car and the kids have their teas n i live like 6 miles away from my doctors so the only time i can get to a doctor is by appointment. so please any adice is grateful