Lots of things can change recall. Stress is a big one, but the biggest is sleep schedule. A simple change in sleep schedule can cause a huge change in your recall. I would recommend getting your recall up as high as possible (preferably 5-6 long dreams a night through siphoning through these and finding which works best for you:http://www.dreamviews.com/dream-sign...ompendium.html

After you get to 5-6 long dreams a night, even stress can't take more than 2-3 dreams away. I would also recommend using my DJ system in order to find out what recall techniques you used as well as LDing techniques, because they compliment each other well and the system can show you what changes what, for you specifically.

Good luck on dreaming.

Also what scionox said about recalling the day is a very powerful technique if practiced consistently.