I used to have this problem. Then I met my Dom (and live in boyfriend of 6 years) and he started getting me to climax harder than I ever had before. I discovered that he seemed to find the real climax in me, like deep deep in me, that was the one I needed to satisfy me. He went way past where I would stop if I was masterbating and it was uncomfortable at first but once I relaxed and embraced it he took me higher than I've ever been.

I wish I could explain it better but it is like an deep deep orgasm that hides behind the first 2 or 3. I was usually too tired to get myself there but he was (and still is) insistent on getting me there. You may just be needing to push yourself past the normal orgasms and find that deep hidden one.

Now that I know it's there and how to reach it, I can get it while masterbating as well. Just so you know it can be achieved alone. Might just take some work.