Dan, as others have said, the learning is all part of the fun, you're still flying.
Like you, I had many instructors, 11 in total! and in hindsight I could've shaved at least 20 hours off my total just from the overlap every time I had a new instructor. It took me two years to gain my PPL, but I didn't care, I took the view that it's my hobby and will still be my hobby when I eventually got my licence. I don't regret the time and all the hours it took to achieve that as it was all fun....even when it wasn't! (if that makes sense).
I too struggled with navigation, i'd be enjoying myself and the view outside so much that i'd forget to actually check the DI, or basic errors like inadvertently turning whilst looking down at the map, only to look up and not recognise where I was. Its something I laugh about now, but was frustrating at the time...and I doubted myself because of it too. But slowly and carefully, I analysed what I was doing wrong each time and worked on it.
There is no need to put any other pressure on yourself other than your desire to eventually gain your PPL.. it doesn't matter how long it takes or how many hours go in your logbook. it's all flying!!!!!
I hope you stick with it, it's one of the best things I've ever done in my life....if wife and kids is 1st and 2nd place, then flying definitely competes for 3rd !
Good luck.