I was at a school where I wasn't the only Further Maths or Physics student (there were 4 FM students and 7 Physics students) but (and not to toot my own horn here) I was the only one really working anywhere near my level. I'm the first successful Oxford applicant to come from my school (although it is only 9 years old at this point.) So I get you.
Competition with others is not a good motivator, as you are finding out. Self Competition, on the other hand, was part of what got me to where I am. I kept a graphical record of my past paper marks for every paper I did (and I did all of them, over and over again on the old specification.) My goal was never to beat my class mates. It was always to beat myself.
Having Oxford as a goal was also a real motivator. You have to work very hard to get in, and it is a great honour if you do. Making yourself excited over the prospect of Oxford could be useful, to keep yourself focused.
For physics, I recommend the CGP revision guides specific to your exam board, and doing lots of past papers. I got an A in physics in the end, but I do believe if I'd done more papers (I was focused on Further maths as I needed the A*) I would have perhaps gotten an A*.
It comes down to self discipline, and finding enjoyment in the subject you are studying.
Also, My proper study didn't really start until I got my Oxford offer, all things considered
Focus on the PAT (you can prepare without guidance, believe me, I did it for the MAT. Got a 48, but still got in?) Then if you want interview tips,
check out my article. If you want further advice, just ask.