[song] writers-block---- help!

i have a question for the whole world to respond to... even though i know i'm only going to have like one or two people comment on this (but thanks in advance to the one or two people). ok so--is a song worth writing if you have to "force it"? for example: i have a sweet guitar part completely finished, but the words arn't working so well. i've made up just under a-gillion different melodies and they all sound okay, nothing just fits together like it should. all of my songs have pretty much written themselves, but i've had [song] writers-block lately. i've hear that the song "margarita-ville" was written in like 5 minutes. and look how much people like that. (for the record, none of my songs are that lame). i'm not saying that i should just make it up all at once, but i can't decide if i should just drop the whole idea and move on... or stick with it until i get what i want. I wonder if the 'best songs' are written in a long, slow, thought-out process, or if they just write themselves. hm, being famous is harder than i thought.
-steve