Writing Process

I have been brainstorming for this short paper for about a week now. All weekend I came up with some topics I wanted to talk about, managed to form some main points, created an introduction, AND formed a thesis (the last thing I do before I begin to write). So things are going great...UNTIL I go in to class yesterday and we begin discussing counterarguments. I am sitting there and can not come up with a counterargument for the life of me.
Of course, I then think of a counterargument for a totally DiFfErEnT paper topic. I quickly write down some main points for this new topic and the counterargument I had come up with. After class I go in and talk with Professor Ambrose and now the trouble is finding a thesis for my new topic. And that is where I am now. Trying to come up with a thesis for my new paper.
Does anyone else have this problem?? Knowing what you want to write about, having evidence and points and a counterargument...all that JAZZ and then not being able to write a thesis that brings everything together? Guess I'll start writing and just hope it comes to me...