Hello there, Flexon has shown to have some nerve related side effects. These will be like you described tingling along the back of your leg or altered temperature sensations in peripheries. If you have had back spasm and a lumbar disc surgery done I would urge you to do back strengthening exercises under physiotherapy as well. In the long run that is what would heal you instead of medication which has a temporary pain relieving effect. Since you said you are obese one alternate form of exercise is swimming. It reduces the stress on your knees and back and help you build strength gradually. Even if not full fledged swimming walking around in the shallow end of the pool will also be a very good exercise. Hope this helps, Wishing you a speedy recovery from back pain