That just sounds like the normal up and down cycles of the game. Some nights you can't do a thing, other nights you're golden.
If I were you I wouldn't be so worried about K/D. I'd get into whatever I'm comfortable in and just go mix it up (within reason... one on one to one on three or so). K/S, K/H and KH% are all part of the fighter mix too and I'm sure you want to get to a point where you can pull them all together.
When I was learning the plane-set, I found commonalities in my flying style and in the planes themselves that could be applied across the plane-set. Then I stayed within those bounds until the situation dictated that I try something else. It's kind of like an NFL team cutting back the playbook and getting back to basics. Even then, one night I was the wonderkind of a certain AC and the next I was junk in the dirt. It takes a while to learn the idiosyncrasies of all those planes. I still don't know them all like I'd like to but using this approach I feel comfortable that I can have a successful flight in just about anything.
Don't let it bother you. Keep at it and keep having fun.
