For what it's worth my guess is that you have several things going on. Girls are ageing, maybe a too much nitro, and as others have mentioned make sure your ph is correct. No one likes to think about it... but make sure your meters are calibrated. I say that because this was a crucial error, I made on my 2nd grow and it started a devasting downward spiral. Also, give the girls what they want when they want it.
Not much I would do now except flush, let almost dry, give a little Bloom and Micro around 500ppm and see what happens. Really... not a bunch to do at this point. Just realize that pushing nutes from middle of flower can lead to some bad tastes. Good luck. Peace!๐๐๐