First of all 'Congratulations'o on your little girl.......There can be lots of reasons why this is so!
So keep it simple, the ultimate formula is.....if you want to loose weight, you Must have the desire. after that the calories 'used or burned in a day' must be more than calories 'consumed (eaten) that day.
But of course in reality it's not that simple......there would be no weight-loss industry, if it were that Simple.
We have to overcome things like......'bad eating habits' (which could include portion size problems, snacking between meals, fast food too often and not enough fruit and veg in our diet) and lack of support from partners and family.
in my experience a great way to start, is to firstly find out where the problem lies.
A food diary is a great tool here......don't buy anything.....just note it down (put it in your phone... we all seem to have one permanently attached to us these days). Every thing that goes into your mouth, note it down.
Make a plan to do it for one day and be meticulous....absolutely everything you eat and drink, for the day.
Now one day may not show you where you could improve, but I'm hoping it might show you that a diary isn't too much trouble.... the real plan is to do it for a week.
After that, if the problem is obvious (too many calories or not enough movement) then Make and stick to a plan.....Get help if you have too. You can't keep to a plan that you haven't got.
I really hate parts of the weight-loss industry that peddle the myth "Oh, it's Not your fault". What BS.
Every day you make decisions about the health and well being of your baby girl, and I'm sure you do it to the best
of your knowledge. Make enough Right choices for your own health and success is assured.