Your DJ doesn’t improve the frequency of dreams. Like you already said, you have to remember your dreams. Everybody dreams several times every night, you just have to be motivated to remember your dreams, and keeping a DJ is the best tool for this. Don’t worry too much about short entries, DR is a matter of practice. This is an excellent guide about DR and keeping a DJ.
You’re on the right path, you even had two LD’s this night, no matter how short they were. 
Improve your DR by keeping a DJ, continue with the RC’s and then try out some techniques when you feel like you’re ready for them.
It could indeed be a reflex of your body that you woke up from your LD’s, maybe you were close to waking up anyway.
The last thing you described where you weren’t able to fall asleep again was the state between asleep and awake. When this happens again naturally, just remind yourself slighty that you’re dreaming (like a mantra), maybe you can even pick one of those dream images and let it evolve into a real dream (hopefully lucid 
).
Keep it up!