Bf3 runs slow after playing for a while

Hello, this problem has been occurring since last week. I start Bf3, it runs very great on AUTO settings. (A mix or normals and highs). The game runs at about 50-80 FPS But then after playing for about 30 minutes. The Fps drops to an unplayable 5-10. I tried all settings and this keeps occuring. My temperatures are as follows: GPU: 51C Core 0 : 52C Core 1: 55C. This is before the lag. During Lag: GPU:55C Core0: 54C Core1:57C.
Here are my specs:
GPU: Nvidia GeForce Gt 525m
CPU:Intel(R) Core(TM) i5-2430M CPU @ 2.40GHz, 2401 Mhz, 2 Core(s), 4 Logical Processor(s)
Model: Satellite L750
RAM: 6 GBS RAM
Installed latest RECOMMENDED driver for GPU
64-Bit Windows 7 Home Premium
This is only fixed after i restart the laptop.
Anyone know why this is happening? How can i fix this? Thank you