What you are describing seems perfectly normal to me. Keep in mind that it can take a long time to develop new habits. And anytime you are in a performance situation (playing for friends, your lesson, etc.) newer progress is going to fly right out the door. It is part of the process. And to make matters worse, we then become aware of every little detail. That awareness becomes concern in a performance situation.
The key is learning how to divide up two different states of mind. One is what sounds like exactly what you are doing. You are paying attention to everything. You are becoming a scholar of the guitar. You are becoming more and more aware of smaller and smaller details. This is a very good thing. Keep it up.
The second thing that really needs to be worked on in performance practice. Myself, I've worked on it, am working on it, and will continue to work on it. Once you feel you really know a piece, it needs to go to another level of practice. You basically pretend that you are performing the piece and you begin practicing covering up minor mistakes. You practice pretending that mistakes didn't happen even though they did. It is not easy at first. It takes practice.
Sometimes I simply tell myself, "this is a performance." I might turn the chair a different direction. I might play in a different room. I might even play for a video camera, or (heaven forbid) another friend. But I don't play for someone else or a video camera unless I have had a LOT of successful pretend performances already.
Very important, it isn't that a piece usually goes from new to old like I suggested above. The truth is, it might go back and forth several times. But everything in the process helps me to learn. I sincerely think I know the piece. As a result, it goes into my old repertoire and I now do performance practice. Sometimes, I am surprised that the piece wasn't ready and I have unexpected problems! Great! I'm learning more about the piece and what it needs!
I couldn't imagine this happening very successful in a lesson right away. And I could hardly ever imagine it happening with something you have only been working on for a week or two. I gently remind my students to relax and that it is a work in progress.
In summary, it is great that you are becoming aware of so many things. It is natural that it has an impact on your performance. Feel better in the lessons understanding that your results sound natural and predictable. If you have old repertoire, start practice performances so that you can BEGIN learning how to handle mistakes in a performance situation. Lastly, if this interests you, you might want to read an old book called THE INNER GAME OF TENNIS, by Timothy Gallway. There was a follow up book: THE INNER GAME OF MUSIC, but I recommend the TENNIS book.
p.s. : don't be afraid to try easier material, too!
Dr. Todd Tipton, classical guitarist
Cincinnati, OH, USA (available via Skype)