40-50 pounds over weight after 5 years of baby

I have to lose about 40 pounds. For the last 5 years I have either been pregnant or breastfeeding and my body seems to hold on to the weight. I used to be the skinny one so its been difficult to swallow not being fit and thin. I gave up on exercise when number 3 baby came. Now the last one is just about done nursing and I want to get back into healthy eating. It's not teaching my kids anything by being like this.