The retainer may be able to hold your tooth in the proper position but you may have damaged your tooth in a different way. I would see your dentist to confirm why there is pain.
What you have is called a cross bite. The lower left tooth is not in the correct position and is severely rotated. I think orthodontics would help align your teeth nicely. This is something that should be corrected sooner rather than later. At the end of treatment, I would request a bonded retainer so the teeth don't shift back to their pretreatment position.
