Buggy FPS

Hey guys basically I'm having weird FPS lags. My OS is Windows 7 Ultimate. Processor : Intel(R) Core(TM) i5-4460 CPU @ 3.20GHz, 3201 Mhz, 4 Core(s), 4 Logical Processor(s) RAM : 8 GB Graphics Card : Geforce GTX 750 Ti 2GB

The FPS is always lower than 60(59 and below, and the game works as if its 30 fps, teamfights 40 fps or lower) , which is annoying. I think i should be running 60 FPS Smoothly, even with very low quality its the same, I only have this problem with League of Legends. It started today. Please help anyone.