You could join your local Pushymothers group. They are mums who walk together with their pushchairs for exercise and company. They are on the internet. If there is not one near you, you could try thinking of everything physical you do as exercise. This way you won't worry about not being able to get to the gym. Mums of old did not need the gym! Take an honest look at what you eat too just in case you are snacking instead of eating a balanced diet. All the best.