Yes, I've suffered through this too. I've been blogging for past few months and keep on checking that, Why there are not any ads on my blogs? But finally got my answer through a video on YouTube. Within 5mintues your blog will start showing ads by trying these easy steps. But before trying these steps make sure you get Adsense approval for your site first.
I don't want to write anything about this topic but want to show you the video which will really help you to start putting ads on your site.
Hope this video or this blog help you to start earning by putting ads on your sites. If you do have any question in your mind then do let me know by commenting below and will try to answer you ASAP.
Your Writer Buddy,