FPS drop for no reason

Hello all, I have FPS drops :/ I usually have 200-235 FPS but from a week I have FPS drop. When I start normal game 5v5 I have 200 FPS at the spawn and after 2-5 mins comes the FPS drop 50-30 for no reason! I got my updates, everything I tried to low my graphics with VERY LOW GRAPHICS I have 50-30 FPS drop I have 4gb ram 1600mhz and 2gb video card and... is impossible to be from my PC i opened Task Manager and there is nothing too..its just from the game fps drop from a week I don't know what to do. Any ideas to fix this shit?