How does this happen? Are THEY watching what we do online ?

[NONAME]

I don't understand this.
One minute I will be answering questions on a Law & Ethics section of yahoo answers, or some other forum.

The next minute I'm getting advertisements on facebook and youtube about the Law, and "In need of a Lawyer?" video advertisements in between my Youtube videos... Which I HAVE NEVER SEEN BEFORE. First time ever. The advertisements are usually about cleaning products or something else random.

Those 3 websites are NOT linked, they are separate, and they are all 3 used with different emails.

So how do the other 2 websites know that I was answering questions on a Law & Ethics forum?
Please tell me.

Is the government watching what we do online?
And please don't be rude. I can't help I get paranoid.