problem: low post engagements
What if nobody "likes" your posts?
"What Do I Do about ..." Low Post Engagements??
You can save yourself some headaches in analysis by deciding ahead of time which posts will be eligible for "paid" promotions, which won't, and how you'll make the determinations in each case.
There is no point in even trying to understand an individual post's "performance" until you have established a baseline for your account, controlled for platform and post type.
Sometimes you may want to sponsor/promote a post that is already performing well; this isn't necessarily a bad strategy, but you'll have to take the ad's origins into account as you perform your next round of analytics or you'll end up confusing yourself six ways to Sunday!
If you haven't established a baseline, your performance analysis is running on "vibes," not data.
Not all audiences spend the same total amount of time & attention on social media ... nor do all audience members participate equally in comment threads, Retweets, and other forms of engagement with posted content.
Calibrate your expectations to your audiences' habits.
^ Which, by the way, you cannot do without studying those same habits.