Help hlp help any guys girls out there?

HEY AM 25 YEAR OF AGE I HAVE A FIANCE AND WE HAVE ONCE IN A WHILE I HAVE A 7 INC PENNIS BUT WHEN WE HAVE I DO HER FROM THE BACK HURTS HER AND FEELS PAIN AND ITS A TURN OFF FOR ME CUZZ I LIKE TO GET INTO IT AND SHE BY DOING THAT TURNS ME OFF AND WHAT CAN I DO OOR DO I NEED TO MAKE IT SMALLER OR BE SOME ONE THAT CAN HAVE GOOD WITH ME HELP ME OUT