That's actually pretty normal from what I've heard. $ raises and lowers with the seasons, and also depending on your niche and depending advertiser inventory, a lot of which is out of your control. Have you noticed your overall view count for the month is lower than previous months as well? That may be a correlation, but from what I've heard it's pretty normal for it to decrease at times.
Think of it like this, YouTube probably have a set amount of advertiser "inventory" (how many ads an advertiser has budgeted, so maybe an advertiser wants their ad to appear only in America, and they want it to be seen 500 times. then you might have Coke who has a higher budget so maybe they want their ad seen 1 million times... and another company with their own ad etc.... collectively, that's the "inventory" and if advertisers have less inventory, there's less ads to go around meaning ads might not appear as often on your content... it gets pretty complex and complicated after a while, but this is my understanding)
You can't necessarily do anything to increase the $ you make, outside of making content that more people want to watch, that in tern, means more ads play per view, meaning more $
But at the end of the day how much you make is pretty much out of your control from my understanding, so it's nothing to worry about.
BUT, if the topic interests you, you can definitely research and learn more about advertising and how advertising is budgeted, how advertising is divided up around platforms, how advertising is targeted based on niche, or demographic, that will give you more insight on how the business side of advertising works. Demographic will also have a part in how much you make. Beauty and makeup etc, and tech make more $ in ads, because advertisers like to target that demographic of say 20-40 year olds who actually spend money on tech/makeup etc...
My drawings of dinosaurs are going to have a much more limited advertising appeal based on my demographic, people drawing dinosaurs are less likely to click or buy from the advertisers that show up on my videos, so advertisers are less likely to target "art" "dinosaurs" "people interested in dinosaurs" as demographics to target.
You CAN control those elements more, but you have to ask yourself if you WANT to target those kinds of demographics.
And of course, you can always diversify and not just focus on whatever ad revenue you might get from adsense.