As a teacher, I'm just going to chime in and say there's no timeline on education. If you do fall behind, there is nothing to stop you going back to education and catching up later on. I know nobody wants to do that, but in reality, a couple of years is nothing. Plenty of people take exams as adults. My brother teaches in what we call a "grind school" in Ireland; it means he gives extra tuition and so on and he has adults in their 30s and 40s taking exams in subjects they didn't do for their exams the first time around or planning to go back to university to get extra qualifications. I know school is a very significant part of a teenager's life and it is important, but it's not quite as important as it's sometimes made out to be and it's certainly not a "now or never" scenario. The fact you are taking it so seriously means you should be fine.

Sorry to hear you are dealing with all this, by the way. I hope your school knows so they can support you.