New(ish) PC's Gaming Efficiency Degrading Over Time

[tomfoolery_03]

OS: Windows 8 64-bit
Model: Toshiba Satellite S55D-A
Processor: AMD A-10-5745M APU w/ Radeon HD 8610G (4 CPUs, ~2.1GHz)
Memory: 8192MB RAM
Page File: 5816 MB Used, 2851 MB Available
Okay so first of all I understand that my PC isn't particularly powerful by any standards, which is to be expected from a budget laptop that isn't(?) designed for gaming. However, I do some casual gaming sometimes, and I've noticed that the PC's ability to run certain games has decreased. For example, when I first got the PC in December, I could play Skyrim on medium settings while getting 40+ FPS, but now I can't even get 30 FPS on the lowest settings. This has happened with other games such as Warframe, Counter Strike: Global Offensive, Team Fortress 2, and others. I've scanned the PC using three different antivirus protection services (Norton, Avast, and AVG) and all scans have come up negative for any problems. I've also defragmented the hard drive nearly every day, to no avail. If you can help me, I would be very appreciative, but if not, then I understand.
Thanks for your time!

 

[Onus]

Has it become clogged with dust over time? If it is less able to cool itself, it may be throttling.

 

[tomfoolery_03]

I honestly am not sure, nor do I know how I should go about checking that, or even how I would go about cleaning it if it is.

 

[Onus]

You would use a pressurized duster. It may be enough to aim it into the exhaust vents, but would probably be better to remove the back and clean it more thoroughly.