Vauxhall Corsa Petrol Filter ?

I Have A Vauxhall Corsa, &&Every Single Time I Get In To Start It, I Have To Sit && 'Warm It Up' For Around 5Ish Mins, (Or It Stalls) Even In Hot Weather, My BoyFriend Says Its Because Patrol Seeps Back From The Engine Into My Tank ?? Or Somthing ??&& Also When Im Driving All Of A sudden Sometimes ITs As If The Carr Losses Complete Power, && Petrol Doesnt Get To The Engine && Slows Down A Little Then A Second Later Is Fine? Do I NEed A New Petrol Fitler ? OR..?
Please Help =]
Thnkyu x