Losing weight is just not about exercising. It is about both exercise and diet control. Along with that, since you had two miscarriages, you may be having low thyroid function or polycystic ovary, anemia, or diabetes etc which are contributing to the weight.
Hence, first rule out all these problems in discussion with your doctor along with requisite tests. Then avoid excess fat and excess carbohydrates from your diet. Eat plenty of green leafy vegetables, fresh salads without dressings, fresh fruits, clear soups without cream, lean cuts of meat, egg whites etc. Reduce portion sizes gradually. You can use the free available calorie counter and weight tracker on MedHelp to plan out your weight and diet. Along with that, do exercise which you can. Walk to work, or climb stairs or go for swimming. Consult a physiotherapist for your back exercises. Hope this helps. Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.