Well...

Sound very similar to the same probs I was having, not exact though.

Turns out my pH was screwy and it was causing a nutrient defficiency. Mine was most likely a Phosphorus def though, kinda hard to say cause my girls are looking way better now but I'm still not all the way outta the woods just yet.

I had to up my Phos and get my pH back under control. pH, IMO is prob gonna be your best bet to get back into shape.

Some of the vets should chime in when they have time, wait to see what they say to be sure though.

BTW, I believe a 18/6 light cycle is best for auto-flowers but I believe it might vary by the strain. Some quick google search and a lot of comments saying 12/12 will diminish your yeild and stress some auto's...