I never had flex before I took apart the fork and I have tried everything (almost anyway) to fix it. I have tried compressing the fork and tightening the screws, tightening the screws non-compressed, tightening the screws very little, and I eventually just put it all back together and walked it into my shed.
I believe this type of flex is called fore-aft flex or forward flex or something to that effect.
I think I will do one of three things:
1. Take the bike over to my LBS and have them fix everything, because there are a few more problems than just the fork flex.
2. Buy a spacer that'll fit around the spring and inside the fork tube to prevent the tube from moving back and forth.
3. Deal with it.