I think the difficulties in the concept of melody come from the fact that a melody is easy to write, yet a great one is hard to find. This is very important. Not every melody you write has to be a great one, so first you should relieve yourself from the stress of thinking you have to write a great one. A good melody is just as good, and since you said you already got one that you really like in the verse. You don't necarrasily have to out do that one in the chorus to get a great song. Also the more you write the better you'll get, but you have to start somewhere. Can't walk before you crawl. So just continue writting even if it isn't as great as you want it to be. This is the only way you'll grow. Strive for better but don't hold yourself back from practicing the craft.
Try humming along with the melody you already have and launch off of that to see what you come up with. A good melody in a song isn't the fact that each section of the melody is awesome, but that it flows in a pleasing continum. Sometimes if you just let things take their natural movement, something really good with come out of it.
The important part melody plays in music is feeling. Melody ultimately sets the mood for the song. It has to, because to musicians and non-musicians alike it's the most paladible thing to the ear. Everyone connects with the melody. So relax and try to feel the song you want to write, and play off that feeling. Alot of the times when you do this, the melody (and other ideas) will just fall into your lap.
Everyone at one point or another has felt the same way you do now. I know I've written songs and gone back and listened to them and gone, "what the heck was I thinking". And it gets tossed. I've only kept a small fraction of the songs I've written due to this fact. It's just a process we all go through. ;)
"My whole life is a dark room...ONE BIG DARK ROOM" - a.f.i.