Macbook is extremely slow, lags, and glitches, unresponsive.

My macbook is about 7 months and recently out of no where it has been freezing, being very slow, takes long to load videos etc. When I change pages the screen will freeze and become black and distorted. It is not just when I am on the internet either, but when I am opening or closing applications. Some people have said try closing applications sometimes it slows everything down, but I have tried that and it hasnt helped. I rarely turn off my computer, and always have it plugged in, i dont know if that has any effect.

I often have to force quit out of safari when switching from pages or clicking on links. And just yesterday I was on a page where there was a link, but I did not click the link but switched to my favorites page, then my screen went black and for about a second an image came up of what the link to the website would have been.

I have tried using onyX to clean up my computer, but I do not see any improvement.

If anyone could help I would be willing to pay over paypal, I really do not feeling like paying apple to help with me with this when I doubt they can.

Thanks