help!!! grades declining over past three years

My English, science, and math grades have improved and/or stayed steady as A’s and A+'s over the past three years. However, my history and foreign language grades have gone down from A’s to B’s from grade 9 to grade 11. This may be because I’ve gone from:

Honors World History (9) - 92
AP World History (10) - 90
AP US History yikes (11) - 85

French 1 (9) - 96
French 2 (10) - 94
French 3 (11) - 87

Classes just got harder and harder. I have little interest in history and French would be my third language, but I feel like I shouldn’t have let those things stop me from getting better grades. Next year I will NOT be taking history or language courses - I’ll be taking AP Calc, AP Stats, AP Comp Sci, AP Physics 2, and AP Literature. My GPA as of right now is a 3.8 unweighted, or 4.2 weighted.

My top school is Northeastern University and I’d like to study mechanical engineering. How hard will this hit me??

Some tips:
http://talk.collegeconfidential.com/high-school-life/2026961-what-to-do-when-you-arent-doing-well-in-a-hs-class-p1.html