Lower back pain, l4-l5, l5-s1 disc bulge

Mechanical reasons contribute to majority cause of low back pain. Since it's almost an year, you need follow up visits to review your condition with the Physiotherapist. Research evidence points out that normal people who haven't had any history of back pain too presented with disc bulges in MRI. But in such people the back muscles were well toned and they had an active lifestyle. So don't worry and go entirely by the findings in MRI.  Considering your age, it's highly likely to be related to bad posture. Carefully observe for factors which causes pain and which alleviates it and share with your Physiotherapist. This helps in gaining more clues on your body biomechanics. May be your exercises need further progression or modification. In some cases, when the patient starts a more active lifestyle, engaging in some active physical workouts like games, the symptoms disappear.

Observe closely for factors which increases pain. If sitting hurts, do some workstation modification for better ergonomics like proper back support.