I was very similar to you when I was 17, although my GCSEs weren't as pretty as yours! I'm 24 now and if there is one thing I could go back and change it would have been to spend more time dealing with things back when I was at school.
If you have to spend this year working through anxiety, A levels can wait. Your GCSEs aren't going anywhere. Give yourself a break, talk to your parents about having time out of school. Keep taking the anti-anxiety medication, those things can often take time and there often part of what helps, rather than the quick fix we all wish they were. As others have said, Young Minds are brilliant and may be able to advice you on any other services you can access in your area.
I would also second writing, or typing as is my preference. Sometimes if you just start writing, you'll end up getting things out that take you by surprise.
Check out Kati Morton on YouTube, I swear that woman is my hero, her videos got me through a lot of tricky times and I found loads of useful advice.
Any kind of mindfulness is good. There are meditation apps, which some people love, but I never had patience for. I am a huge fan of colouring, it helps me distract and just generally feel calmer/less numb.
Think about things you used to enjoy or if you ever made 'bucket lists' as a kid, what was on there? Try doing those things, even if it's just for a small period of time and you don't particularly enjoy it to begin with. To give you an example, when I was 21, having dropped out of University for the second time, I started doing martial arts, because it was something I'd always wanted to do and never done. I had to drag myself to classes. Some weeks, that one hour was literally the only thing I did. It was scary and in the beginning, I still felt numb, but at least I felt like I'd done something. Fast forward 3 years and I can honestly say the decision to start that class was the turning point in getting myself back on track.
Sorry for the long post, I hope something in there helps. This will get better! Being 17 is hard!