I have a small gap starting in my bottom teeth although I have a permanent retainer on the bottom, what should I do? (Photo)

If you have a retainer that is permanent on the lower arch and still noticing a gap, most likely the glue has come loose and therefore gap is forming.  Have your dentist take a look at it so that he can rebond the retainer.

I would definitely visit your orthodontist to have this evaluated.  In general, a well-fitted retainer should limit rotation of the lower teeth.  However, if space is forming there may be pressure on the teeth causing them to move forward.  This could come from the retainer itself (they can be bent or distorted during eating), the tongue or some other habit (chewing on pencils, bottle caps, etc), or even the way the teeth are biting together.  The sooner you can address the movement the easier it will be to fix!