I'm not sure that there is a 'right' way to feel after masturbation. But for me, I normally feel relaxed afterwards. I sometimes masturbate when I go to bed because it makes it easy for me to fall asleep afterwards.
I wouldn't say that I feel "long-lasting pleasure", but I usually enjoy it and that's good enough for me.
Yes, you could be stifling your experience because you don't know how to focus on your own pleasure. It is easy to fall into the habit of seeing sex as a service you provide to a partner. But it doesn't have to be that way!
Do you know how to pamper yourself in other ways? Can you take yourself out on a date, or enjoy a hot bath or your favourite food like AnxiousAna suggested? Maybe if masturbation feels pointless, you should find other ways to give yourself pleasure or love until you are more comfortable with the idea. As Ana said, you’re important – with or without a partner!
No diagnosis, lots of opinions, and a bunch of issues that I haven't quite figured out.