FPS Drops in game

When I first started playing, i got 120fps on high settings. But, my fps started to drop, until i eventually put it to low settings a couple of months ago, where i capped the fps at 60fps and it stayed at 60fps. But now, on low settings, i get a constant 5-30 fps with many drops. Not only that, but when i dropped it to very low, my fps got lower! And for some reason, when i play with 30fps, everything moves in slow motion.

(i tried very high for fun, which actually made my fps go to 50 lol. but i cant play on that with complex animations)

How do i solve these fps drops?

Specs: Lenovo G50-45 AMD Quad-Core A8-6410 APU AMD Radeon R5 Graphics Windows 8.1 64bit 6GB Ram 500GB hard drive at 5400 rpm