Hi there,
I think it is fantastic that you are thinking about the future; it shows that you care about your next steps and where you will end up in the future. However, I agree with your conclusion that your current habits aren't healthy, i.e. almost obsessing over A levels and university. You are only in Year 11, so I suggest that you take a step back and focus on your GCSEs. As you said, perhaps excessive use of TSR has been exacerbating your anxiety and worries about the future. It is good that you have some form of distraction (sports), keep on doing this! I assume you are quite academically minded, so it can often be hard to distract yourself from, well, academics, but as long as you have some form of distraction or leisure time, it should help you stay away from worrying too much. All I can say is try to live in the present, because A Levels and university aren't going anywhere just yet!