You need to start with back strengthening exercises ASAP. Due to age related osteoarthritic changes you are getting pain on long standing. watch out your posture and make sure you are maintaining the lumber curve while standing. Take breaks and avoid too much of stress on your back. Keep a small step under your one foot to relieve the pressure. As of now , it is all possible to rectify the issue. Once you get good strength in back , it won't trouble you for long but if ignored this might escalate and put you in trouble.