Dear Vince,
Thanks for noticing my efforts to liberate the most frequently experienced universal sexual outlet, masturbation. Now, what the hell are you doing with your dick that doesn't produce an orgasm? The fact that you have nocturnal emissions or what is better known as "Wet Dreams" demonstrates your plumbing is in order. So I figure your problem might be psychological based upon sexual inhibition. Perhaps some awful repression is lurking in your mind.
I assume you are young, teens or early twenties, and without sufficient information, but I can only guess. While there's nothing wrong with using olive oil or any cold pressed nut oil, or for that matter, a big glob of spit to get started, your uncircumcised penis actually makes masturbating easier as the foreskin is somewhat self-lubricating. Maybe you've developed a lousy technique for playing with your peter. Too hard, too fast, too worried, too fearful? When you say, "At least, it feels good at first. After a while, usually when my penis has been erect for a while, it begins to feel uncomfortable." This makes me wonder if your foreskin is too tight. If so you might want to see a urologist who can release it. This does not require a full circumcision, just a minor adjustment.
Or you can just continue to masturbate and keep trying to move through the phase of "uncomfortable" and stretch your own foreskin. Breathe into the sensation and stay with it a bit longer each time. Similar to a young woman who is learning to stretch her vagina by gradually opening it up with her fingers while using a clean lubrication like my Sweet Almond Oil, you will be stretching your foreskin by pulling it back a little further each time. Your last suspicion about lack of spontaneity is BS. When something feels as good as an orgasm, it doesn't have to be different every time. Let me know what happens.
Betty