all i have to say is work hard...i love math and science and i get very high marks (high 90's at enriched level courses) but in English i don't do so well. I was getting low 70's, but i pulled my act together...i stopped doing the things i liked. I would study hard..test myself on the stuff i did and if i remembered it all i would treat myself to something i like to do...but if i scored badly i would study more.
None of us can tell you how to motivate you, it's ur life and your decision...nothing we say is going to change what u do.