What Is The Treatment For Erectile Dysfunction?

I AM 45 YEAR OLD MALE. I HAVE PROBLEMS IN ERECTION,THE ONLY PROBLEM IS WHEN IM WITH MY PARTNER IT TAKES TIME TO GET STIFFNESS. AND MY PENNIS DOES NOT GET STIFF ENOUGH LIKE IT USED TO..ALSO AS SOON AS I START DOING IT MY PENNIS LOOSES ITS STIFFNESS AND I HAVE TO GIVE IT A MINUTE TO GET HARD AGAIN..... HOW CAN I OVERCOME THAT...IS IT BECAUSE I MASTURBATED A LOT AND EVEN NOW I MASTURBATE LIKE ONCE A WEEK. THANKS.