What kind of app you are making this much amount of impressions with? Coz your numbers and region of users is just perfect to make minimum 1k$ per day with 3 million impressions. And has your admob earnings dropped recently? Or are you getting better results before? In such cases you should always use mediation.
Definitely use different ad networks in addition to adMob, but be careful - some might get you in trouble. Big companies are a safe bet though - twitter’s MoPub, Amazon’s ads etc. Maybe that appodeal, they seem stable enough, but I haven’t tested them yet myself.
its kind of hard to tell what you SHOULD be making, I see that you’re trying to show ads on every possible request which is not helping your eCPM overall. The way admob works (i’ve tested) is that if your CTR is good, and you don’t over do it with ads, they send better/higher paying ads your way with better cost per click.
my eCPM is very strong compared to yours even with high amount of impressions. but my request/impression rate is about 20% and ctr is over 4%.