Weight gain after stopping the pill?!

I had been on ortho tricycline lo for 6 mths after I had my son I stopped it last month hand my period last week and it's still kinda here but over the past 3 wks I have gained an unexplained 3-4lbs and felt bloated... I count every calorie and exercise regularly check out my diary... The only thing I can attribute it to is getting off the pill.., anyone else experience this and any ideas to combat this weight? Please I was at a weight where I was happy and now ughhh! So frustrating !