Heh, sounds pretty bad.
Are you using Optifine and have Chunk Updates Per Frame set to 5?
The i3 (even the latest version) isn't too powerful, chunk generation might be a bit too much for it.
optifine helped a little; my fps went from 4ish to 15 - still wasn't playable for me, and I didn't know how to set the chunk updates per frame, so I ended up deleting my .minecraft folder in C:\Users\[name]\AppData\Roaming\.minecraft. that seemed to solve the problem. thanks for the advice