The exercise which helps with my lower back pain is the one depicted here: https://helenaciampolini.com/deitar-com-as-pernas-contra-a-parede-um-alongamento-simples-e-otimo-para-saude-do-seu-corpo/  . 

Basically you lay on the floor with your back to the ground, and raise your legs to a wall forming a 90°/ L shape. It is important for the legs and the bottom to be pressed against the wall.  then, try reaching with your hands to your feet toes. You will feel the back stretching and relaxing, and the pain should be mitigated in a couple weeks.