Forums their traffic levels are too low to really bring in a good income by ads. Google gives you pennies, unless you have over millions of monthly views - but that level isn't reached in a couple of years, it takes decades. And if you haven't gotten to that level today, then it's likely you never will. The traffic for forums are declining by the day, that is just a fact.
I don't understand people with new forums, just immediately slapping on google ads. Not only does it make you look desperate for money, it's horrible from a guest/member point of view and you'll likely drive away more traffic than you'll gain. Stop doing it.
You can try to gain some private advertising parties, but your site is most likely too small anyway.
So as
@Senkusha says, if you don't have any value for your members, you will die out sooner rather than later. Just because your forum isn't taken offline, doesn't mean it's flourishing.
Do it because you enjoy it, not because you're desperate for money.
That is the hard truth.
