How much do you think I'll lose?

I had a baby 5 months ago and really trying to lose the baby weight. I was a size 12 before I got pregnant and now a 14/16. I've just signed up to the gym and will be doing 30mins tums and bums cl followed by 30 mins circuits on mon, wed and fri. So 3 hours a week in total. I'm also eating healthily - average day is: bowl of alpen, natural yog with berries, OJ....bowl of veg soup with brown roll...chicken and veg lasgane and frozen yog....low cal hot choc, banana for snacks. How long do you think it will take to get to a 10/12?