The Reverse Sandbox Effect in Google
I have experienced this myself earlier, with search traffic being very volatile in the first six months or so. Here are a few examples of search traffic for sites launched under new domains in 2014:
These sites were launched at the same time and with very similar content and markets. Notice the changes in volume at an average. So don't parade yourself for immediate success as you may yet hit the bunker, to use golf terms.
During this time it's best just to wait it out and throw money at Google via AdSense.
The Reverse Sandbox is real
The sandbox has been discussed since 2004, but in addition to the sandbox effect, a "reverse sandbox" effect is also claimed to exist.In 2015 I launched a few similar sites and noticed huge swings in organic traffic in the first months. Below are graphs for the search volume for these sites:
The first graph shows a rather consident progression of search visibility, but the second has a much steeper degree of variance in these results.
Like anyone working outside of Google, I don't know how exactly this ranking works. But people as a whole are quite predictable, it is quite clear that the algorithm is lifting up content it deems to be of good quality, but not yet solid enough from a domain authority, link building or other reliability factors.
Real time search
In any case starting up a new site under a new domain will take time. It takes months for traffic to stabilise. But as for swings like this, it's worth noting that at an increasingly competitive content market real time search is increasingly important.
Google has acquired access to the Twitter firehose and is experimenting in displaying Twitter results in Desktop SERPs. Apple also has access to the hose and will likely push it's Applebot powered search results in iOS9 at launch or later during it's lifetime.
If you're dealing in mainstream content such as generic news, you'll need to push your content. Not just wait for someone to pull it.