Why do I have so much Minecraft lag?

I recently bought Minecraft and I restored my computer earlier because my hard drive was all clogged up but it never used to lag as much as it does now. I want to know what happened?

I have an Acer Aspire Series 5552 series

These are my specs:
Operating System: Windows 7 Home Premium 64-bit
System Manufacturer: Acer
System Model: Aspire 5552
BIOS: InsydeH2O Version V2.06
Processor: AMD Athlon(tm) II P340 Dual-Core Processor (2 CPUs), ~2.2GHz
Memory: 4096MB RAM
Available OS Memory: 3578MB RAM
Page File: 1606MB used, 5549MB available
DirectX Version: DirectX 11
DX Setup Parameters: Not found
User DPI Setting: Using System DPI
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Disabled
DxDiag Version: 6.01.7600.16385 32bit Unicode

Added (1). How can I fix it or do something to make it faster?

Guest

You maybe have slow internet connection too ^^

divo

It's the core processor bro.

Someone

It's your processor. Minecraft needs a minimum of 2.4GHz, I believe, to run without lag. Oh, and your RAM needs to be at 4GB.

Kelsey