Most of them must be sabotage clicks, and you need to report them to Google immediately to secure your Adsense account. http://www.dagsensecodes.com/2006/11/reporting-invalid-sabotage-clicks-to.html
something must be wrong here. analyze your site stat to see where traffic coming from and how long it took you to get 5000 clicks. you might have been click bombed or most of those clicks are somehow identified by google as invalid clicks. i suggest you contact adsense support and bring it to their attention before they contact you
definitelly something wrong. did the idea that something might be wrong ever cross your mind? you thought going from 12 clicks to 5,000 was ok?
Well, what you earn depends on the keywords, what the advertiser pays, etc. That could be a lot in some niches and just pocket change in others! But it looks like other DPers say you were click-bombed. So you should contact at once to get it straight (to let them know you are aware of the problem and it was not you).
Let's say you got 50 clicks = $1 $8 = 400 clicks That person clicked on your Ad ~4600 times? each click took him ~1 second to do. He repeat clicked on your Ad and hit Go BACK previous page. That would takes him more than an hour to do that. This guy has a lot of free time.
I guess.. that guy has any sofware..(or) script.. like that.It's impossible to click 4600 times manually...
I agree with The Stealthy One here: it could just be that in your niche clicks don't make that much money. It really depends on whether you have that many clicks normally or not. If you normally have only a 100 clicks a day, and now suddenly there were 5000 - that does make it likely that you were click-bombed. And yes people: if you are clickbombed it means some type of software is targeting your website.
That's okay. Nothing's wrong. It's just that you might be in the wrong niche with advertisers paying low for your clicks