Lower back pain that flares with standing or sitting on the floor, together with new foot joint pain, usually points to muscle and joint strain from your daily strength training and long walks, especially if your routine or footwear hasn't changed recently. It's rarely due to one single cause.
Next Steps
Add a few rest or light-activity days this week, stretch your hamstrings and calves daily, and check your walking shoes for wear. Easing the training load for one to two weeks usually lets a strain settle.
Health Tips
If the pain hasn't eased in two to three weeks, or you notice numbness, tingling or swelling, please see a physician or orthopedist for a proper check.