Do you know what's causing your grades to plummet like this?
Yes. Forgetting anout everything in classes where you need to just memorize (History, Religion), having a stuff resistance in Sports (I can't run 15m and my coach doesn't understand that; he already hates me because he hates fencing), and mixing up constants/equations in Chemistry.
Basically anything that is pure theory bores me to failure. In lab, bio, and o.c., we use the lab and do the practical stuff, with theory on the side.