Laptop GPU core speed locked/capped

Hi.
I have a budget laptop on which i game on,and when I first bought it,it used to play games decently (in my standards).

But later on the FPS on my games dropped suddenly and I did not notice as I didnt have an FPS counter but the lag amd stuttering was evident.
(e.g. Far Cry 4 ran at 30-40 FPS but reached 15-25 after the drop)

I started monitoring my games with MSI Afterburner,and the temps are fine for my GPU.
Later, I realized that the core clock speed seemed to be capped at 540 MHz and went even lower sometimes(my GPU should run at 1024 MHz).Temps are normal for my GPU(59-high 60s) and CPU seems to be working fine.

Please help me find a solution!

Specs(Beware! Not a marvel of technology):-

i7 5500U @ 2.4~3.0 GHz
Nvidia Geforce GT840M (ze Mr.Problem)
8 GB RAM
1 TB HDD
Windows 8.1 Pro

Things I have tried(unsuccessfully):-

1) Updated to newest drivers and rolled back too on some suggestions online.
2) Put Nvidia Battery Mode thing from adaptive to Maximum Performance
3) Using laptop on high performance
4) Checked GPU temps ( they are normal)
5)Turned it off and on again (sigh)

Thanks alot for reading!!