Why Can't I Focus on One Task for More Than a Few Minutes ??

I'm having trouble focusing on one thing at a time.

For example I work from home.

Let's say I'm reading an article online for a project.

After about 1 minute of reading, I get the urge to open social sites like twitter to see what's happening.

Before I know it, I'm scrolling through my feed for sometime and then again return to reading the article.

Another example would be if I'm designing something in Photoshop or editing a video, after a few minutes I'll open FB or twitter, spend some time scrolling and then return to my work.

It's as if I can't stay focused on a single task, even though I live alone and work in a quiet environment. No one interrupts me, and there are no distracting noises or other obvious disturbances.

It's like my legs start to shiver and signals me to shift attention and open some sites.

Why is this happening?

What is this called and how can I fix it?