One of my top teeth appears to me moving ver slowly , being pushed back behind the 2 teeth next to it, occasionally it hurts.. why is this?

Inflammation..: .. Inflammation usually causes pain. It could be from food getting caught, from decay, from the malocclusion, from a change in your bite, or even from periodontal problems. So many possibilities, but without an exam with a radiograph, any answer is only a guess. Consult with a local dentist for a definitive diagnosis.

Not uncommon: Teeth want to erupt and to migrate toward the midline to compensate for the wear our stone-aged ancestors gave their teeth that we don't. If you have a malocclusion with slipped tooth-to-tooth contacts very slight crowding becomes more accentuated over time. Gum disease speeds the process. Ask your dentist to refer you to an orthodontist for an occlusal evaluation.