Try intermittent fasting. Look it up.
I lost loads of weight mainly by watching my calorie intake and made sure I drank at least 2 litres of water per day. I had a really bad back too so the only excercise I did was walking "in the zone" for at least 30 mins per day. That meant I walked fast and really and strode it out whilst keeping my core tight.. This rebuilt the strength in my core muscles and helped fixed my back. Good luck on your weight loss journey.
Choose a form of low-impact exercise that you can participate in without adding stress to your back. Spine-Health suggests options such as walking, biking or water exercise.
Participate in your preferred form of exercise for a minimum of 30 minutes a day most days of the week, as recommended by the American College of Sports Medicine, or ACSM. If long exercise sessions aggravate your back, break them up into smaller pieces: take a 10 minute walk following breakfast, lunch and dinner, and you've accumulated your required exercise. The ACSM does note that weight loss could require as much as 60 or 90 minutes of cardiovascular exercise each day, so make adjustments to your routine in order to see results.
Lift weights several times a week. lifting actually strengthens the muscles of your back and spine, and in time, could decrease your pain level. Also, as you build muscle, your metabolism will increase, assisting you with your weight-loss goals. Ask a personal trainer to show you proper form, and start with exercises that isolate specific muscle groups, like the leg extension, leg curl and back extension
Start a food diary and write down everything that you eat or drink. Look for unhealthy eating patterns. Many people find that they overeat when watching TV or when they're handling stressful situations.
Make small dietary changes, adding one new change each week. For instance, if you eat out at restaurants five days a week, aim to only eat out three days a week, packing or cooking healthy meals on the other two days.
Cut back on empty calories--those calories that you consume that don't deliver any necessary nutrients or that have a large number of calories from sugar or fat. Soft drinks, sugary coffee beverages, candy and doughnuts all fall into this category.
Try tracking your calorie intake along with your food diary. This will help you keep honest about the amount of food you're taking in.