I think you made too many changes to your squad. You said you've sold and bought players, and about 8 players are listed there. So your whole team has pretty much changed, which is never good on the short term, even long term at times. It'll take a few more months for them to settle in, some longer than others.
I'm sure if you look on your assistants feedback during matches, he'd have pointed out your players are still blending into the squad. Plus the players need to adjust to your tactics, just give it time. Maybe one or two positive signings in the summer, with a couple of unneeded players leaving would do you good.
For instance, my first season (At Liverpool, but ah well). I kept Liverpools squad, no one leaving (Except, those on loan, etc) and then I signed Elano for 8 Millon in January. I had good success, a couple of cup wins. Then I chopped and changed things around the next season, off goes Benayoun, Arbeloa, Hypia, Lucas, etc. With a few new positive signings, like Mata, Rafinha, etc. While doing so, looking around for young talent.
Over the next couple of seasons, I assembled my squad. I have now only made one major signing in last two years, and that was Jack Wilshere. This is because I had a good young squad for them two years, with experiance also, think Utd at the moment (But better

). Young players now come through from the academy, etc while finances rise.
My point is there, don't rush signings. Slowly build a squad, Newcastle have a good enough squad for mid-table anyway. I would just strengthen the full backs and maybe a new central mid for them.