I'm also a mum of 3 (2 biological) and I have PCOS, too. Over the past couple of years I have lost about 5 stone (70 lbs), although I still have another 50-60 lbs to go.
As far as kick starting your metabolism, eating breakfast and have 5-6 smaller meals a day instead of 3 large meals will help attain a more even metabolism level opposed to peaks and troughs.
I don't calorie count but I try to make sure that the amount of carbs in grams I have in a day approximately equal to the amount of protein+fibre in grams a day. Go for complex carbs as much as you can, too, things like brown pasta and rice, granary bread etc. This helps with the insulin resistance part of PCOS.
About an hour before I exercise (running, roller derby, or circuit training) I try to eat some complex carbs (usually 1-2 slices of granary toast with some peanut butter and sunflower seeds) for energy during my exercise. I then follow up the exercise with some protein to help build muscles, something like a hard boiled egg, a chunk of cheese or some chicken breast chunks.
(Disclaimer: this is just what I do, and not medical advice lol)
Hope this helps, give me a shout if you want