Can you post a picture of your current set up? It honestly could be a matter of your nose too far up, your seat height or your saddle's fore and aft position being off. And it's not a matter of how much of your butt hangs off the back; you want to have your seat bones supporting your weight. You can't feel it as well on a cushy saddle, but you'll know right away if you try a harder one.

ETA: I want to add that it could be you have a crappy saddle, or if you yourself have a larger frame, perhaps you simply need a wider road saddle. In any case, the best solution to your problem, I believe, is to go to a bike shop and have them fit you to the bike and do a saddle adjustment. Yeah, they'll charge you for it since you didn't buy the bike there, but it will most likely be cheaper than a new saddle.