new mum & wedding countdown!

Hi, I'm a new mum (son is now 5 weeks old). I'm also getting married in 4 mths and my dress (bought before pregnancy) doesn't fit!!! I can't blame it all on pregnancy as I was overweight to begin with. Anyway l have 4 or 5 stone to lose - I don't expect it all gone before wedding!! Before pregnancy I was fairly active and loved weight lifting and kettlebells. During pregnancy I stopped lifting but kept up kettlebells although not as intensely. I had a section so not exercising again yet (apart from short walks) and will prob have to ease in slowly to what I was doing before. I've never tried calorie counting before so this is all new to me!!