Lag issue in minecraft 1.4.2

So basically , ijust downloaded java 64 bit and 32bit , latest , installed minecraft , ( i did force update ) , and first thing when i open minecraft is , i dont have menu sounds , okay... that was weird , i changed settings video stuff ,and i generated new world , ( superflat ) ( overworld preset ) and first thing i know , is that i had 2-3fps for a good while . GODDAMN ,whats wrong with this lag , is there memory leak , or fps lag or something? im using laptop . ( i used to have atleast 30-40 fps , but 2-3 or 20max is kinda madness .. and its superflat! ) , please fix ur game , i really want to play 1.4.2 but with this lag its not possible.