Minecraft Major lag problem?

Okay so there are a lot of problems with it. first of all, i have to keep refreshing the world by pressing F to stop the choppy movement just for a little bit and then it goes back to being choppy. also after awhile it just freezes up and i cant just exit out i have to go to the task manager and exit out from there. also during the lag, when i place a block, it freezes for a second and then when it unfreezes i end up placing 2 blocks. also sometimes the sounds in the game echo really bad. i have tried everything including setting the graphics to fast and setting the render distance to the shortest and the best frame rate option, messing with the infinity and putting the priority to high. I even tried to re-install minecraft completely. IT DOESN'T MATTER. I have no mods or texture packs and i have not attempted to install any. its been like this since i first tried the game. I have a new laptop with windows vista and everything that i have on the laptop is updated to the latest version and all i have bit-defender as my virus protector. (I played this game with game mode on and off and it doesn't make a difference) please help me find a way to fix at least some of the problems i have with this game because its the best computer game i have ever had.