I've faced similar back pain too. First, get your scans done and see if there is a spine issue like disc slips or anything. Also check for Sciatica due to Spine. If Spine is not causing issue, start strength exercises for back and core. Many times, due to excessive sitting, your core and back muscles become weak and can't support your posture anymore. This leads to overworking muscles then inflammation then back pain. DON'T LIFT WEIGHTS OR DO CARDIO because these demand strength from core and back.
There are many exercises that specifically target core muscles, the hip muscles (glutes) and lower back. Start doing them alternate days. Take protien when you exercise. It will take 3 months atleast to get some strength. Also twice a week stretch your lower back, hip muscles too. There are many good yogasanas for them. Google them all.