Major Lag

When I load up the game,the very starting screen is the first show of lag. The moving landscape in the background has been slowed down to about a frame or two every second. It takes a while to even select "Start Game". When there, it lags on until you open the world. But it continues there, with max framerate that I receive in-game is 1-2, especially when loading new terrain. However, when I pause the game, it returns to the 30+ frames that I receive while playing in 1.8.9.