I've used adsense before and it was my 1st way ever to earn money online. I may say that I hit the jackpot because I chose a niche that is not saturated yet and I found a way to advertise and promote it using different and unique methods. I was able to earn $1000 in just a span of 3 months. After that 3 months of excellent income from adsense, my adsense income dropped because the niche that I chose is seasonal and some of my competitor copied the way I promote that website of mine. I decided to sell that website and find other means of earning money online. I may say that, If you want reliable and steady income online, adsense is not the right way unless you're getting 25k unique visitors everyday. It's unpredictable, unreliable and Google's Adsense TOS is very strict that may lead your website from being banned without any noticed from them on why they banned your website. I'm now using CPAlead (it's very similar like adsene) on some of my websites and I found it very reliable and I earn much income from it compared to adsense.
the visitors country is very important! i've notice that visitors from US bring me a lot of money compared to visitors from Europe for example!
Can it be, that Google tricks a litte or better betray us? I remarked that most of the time the first click on ads brings nothing but if there is a second click of the same ads brings much more.
The problem is: You haven't got much search engine visitors. There is too much direct traffic, people who visit your site more often do not click on ads.