Yes, it is very likely to happen as exercise helps to convert fat into muscles increasing your metabolic rate. When you give up exercises, muscles get converted back to fat and your metabolism tends to slow down leading to weight gain. Since, you are planning for pregnancy, you will gain weight during pregnancy which is normal and you should not think of losing weight during pregnancy as it can harm your developing baby. First of all you need to space your pregnancies. As you have said that you have a year old baby, you must try to focus on caring for that child and at the same time try to lose weight if you are overweight now. Only when you achieve a healthy weight, you must plan for a second child. Also spacing pregnancies helps the mother s body in replenishing its stores of nutrients which will have a more favorable outcome. You are more likely to deliver a healthy baby when your body s stores of iron and calcium are replenished and you have a healthy weight with no medical issues. So, think about it as you are still 25. You can wait for a year or two before you plan another pregnancy. It will give you enough time to return to your normal weight. Hope my suggestions will help you in making a wise decision. Take care.