EXPLAIN TO ME WHY I DON'T HAVE STABLE FPS WHILE PLAYING LEAGUE OF LEGENDS?

I just bought this new lenovo G50-70 last week, and I installed league. I thought I would have a better gaming experience with my laptop. Even if I put the settings on 'very low', it can't afford to have a stable fps. Its an i5 laptop with AMD r5 m230 2gb GPU.

The fps can fluctuate depending on what is going on it the game this will happen with any graphic card, hoewever if the fps drops dramatically below 30 that would be unusal