Lower back pain. Of this please help.

Back pain only occurs when I try to get up or move. Walking and all other movements dont cause any pain. Getting up from the bed is when most of the pain occurs. I had left my job 3 months ago and do not have chairs etc to sit up at home so watched television for long hours by lying on my chest and pillows  below my chin to raise my head up so the back stayed bend in the opposite direction a little. I am not a sedantary person, I go to the Gym everyday and do strength training with weights and 1 Hr of cardio such as walking and cycling. However I havent hurt my back during training as I did back exercises with very very light weights for these 3 months. I believe my posture of lying on my chest and head raised + not sitting on chairs + slightly wrong posture even with the light weights may have been the cause of this Please help.