FPS issues

My PC is booty I'll admit that but I usually get around 70 FPS in laning phase and around 35 to 40 when late game rears around and we get more teamfights and it's definitely playable Now it's dipping below 15 and sometimes for no reason. I made sure nothing is breaking or needs to be replaced and all my other games run as well as the always do. Not great but again playable I clear out programs with task manager, make sure my defrags are scheduled around my playtime and such and such. This seems to happen every few patches where my game just starts dying. My load in time is as good as ever and it seems the client is running better for me lately. Anyone else?