Hi roxxie.008
Welcome to the boards!
This is a pretty common experience when you start masturbating - it can take a while to tune into what feels good and build up how intense those good feelings are.
That feeling of being pleased, and then feeling done is probably your orgasm. It's common after you orgasm to want a pause before getting turned on and going again. If you want to draw out how long it takes to get there, then there are two things I'd suggest to start with. First, you can allow yourself to take longer to build up - porn + clit is high intensity to start with, so maybe try something less intense to begin with? The other thing you can do is start paying more attention to how you feel just
before that tingly, "done" feeling, and see if you can change what you're doing so you don't tip over the edge so soon. How does that sound?
We've got a bit more info about masturbation right here if you're interested:
Going Solo: The Basics of Masturbation