I'm in Junior Year right now, and as a person who's ended every semester with A's or above average grades, I feel ya! Everyone knows that junior year is the toughest (to a majority, but be prepared!), and I have like two low C's and a frickn' D in the highest Chem. class available at my school, and I'm ending these with the first semester unless I get better grades on current assignments. Does your teacher(s) still provide you with assignments so you can raise your grades?

Also, I see you have trouble with Algebra. Algebra was the most easiest math level to me which is why I'm ahead a year (half of the high-school students get that choice depending on grades). If you want, I could help you with Algebra stuff :3 Or you know what? Youtube has really helpful teachers that can explain certain subjects, at some times, way more clearly than your schoolteacher, I have to admit.