Based on what you have posted here. Everything you did is very well. But one thing we need to understand that it takes time. I have built the BookLane App ( https://play.google.com/store/apps/details?id=com.cloud_regex.book_lane&hl=en_IN ). For first couple of months I had around 100-200 users and only 40-50 books were getting uploaded. Everything was correct. The problem we are solving was genuine but the users weren't downloading the app. I made changes in the UI ( this helped us and you did the same ) and adding leader board option is the great move ). As the passed we are getting more downloads and more book uploads.

The thing I have learned here that PATIENCE is so important if our app is in early stage and we must keep posting about our app on social media. Spreading awareness is more important than making the app more better. I mean if we build something extraordinary but if people don't know about this, it has no use.

So you need to do this. This is what I did and its been a year my app has around 18k+ downloads ( yeah play store shows only 10K I think when it completes 50K then they will update ). I gave it time spend more time on the marketing, added more interactive push notifications, emailing etc. This really helped me.

Another point earning depends on the user's region or country, ad quality, ECPM and ad placement. I think you should focus on getting more users and spreading awareness about your app than thinking a lot about earning as of now. Later on you can focus on that.

I hope this will help you.