I am experiencing a major lag on my single player minecraft, please help! Game is unplayable and very frustrating.

Hi and thanks for your time, I have just bought minecraft this past week and would easily get 90-125fps on multiplayer. But once I tried to play a single player game after a few minutes it would drop to 0fps and would freeze for a while and then go to around 10fps then go back to 0fps. This issue is very frustrating and my computer exceeds the requirements needed for Minecraft with 8 gigs of ram a Nvidia GTX 560ti and an i7 1600k processor I am confused at what is the issue. I made my own server and it still lagged, and this past couple of days now I will get 0fps randomly on multiplayer. No mods installed. On this issue I am really puzzled because it will run fine for a couple of minutes and then act up. Please any help will be greatly appreciated! Also I don't know if this is related but Minecraft has crashed over 20 times in the past three days since I bought it I added a file but I don't know which one will help the most because of the amount of crashes.