Why does my minecraft lag so badly? (Can't fix it!!)?

Ok, so I have everything as low as it can go. Render distance tiny Smooth lighting minimum Clouds off Performance max FPS etc. Well. I don't know why it doesn't help. I still get 15 or bellow fps. About 2 weeks ago it was fine. Running up to 100 fps. And also, this is only minecraft! My computer is super fast. I don't know why. And don't tell me to download optifine cause it helps not one bit. Can anyone help me please? Also, here is some info about my Alienware. Processor: Intel(R) Core(TM) i5-3210M CPU @ 2.50GHz Installed RAM: 8.00 GB System type: 64-bit operating system Ok, please tell me anything that could help it's getting super annoying and this just randomly occurred out of nowhere! Thank you.