You keep a habit far more easily when you can see it adding up. Not the posting day you planned, the posts you have actually made. Keep a simple, visible tally, one tick for each post, and the growing row does a quiet job of pulling you on.
There is strong evidence for this. Across a great many studies, people who keep track of how they are doing, watching their own progress toward the thing they set out to do, follow through markedly more often than people who do not; and the effect is stronger when the progress is written down where they can see it rather than kept in their head (Harkin and colleagues, Does monitoring goal progress promote goal attainment, Psychological Bulletin). A tick on a calendar is exactly that: progress you can see, on paper, not in your head.
The Christmas run-up shows the pull of a visible count from the customer’s side. An advent countdown works because every day you can see how far you have come and how close you are, and the marking-off is half the fun. You can see this on the Christmas run-up: a visible count keeps people coming back day after day, and your own row of ticks does the same quiet job for you.
So keep it dead simple. One tick for each post, on a calendar you already look at, by the till or on the fridge. Not likes, not reach, nothing you have to go digging for. Just did I post, yes or no. A barber can glance at the week and see the tick or the gap in a second, and that one second is the whole nudge. The aim is not a spreadsheet; it is a row you cannot help but notice every time you pass it.
Once a few ticks line up, you will not want to break the run. That small reluctance is worth more than willpower, because it works on the busy days when willpower has already gone. The ticks are not there to shame you; they are there to show you the shape of what you are doing, so adding the next one feels like keeping something going rather than starting from nothing.
It also pays to look back every so often. On the weeks when the results are slow to show, and there will be plenty of those, a month of ticks is proof to yourself that you are doing the thing. Seeing the effort add up on paper is often what keeps you going when the likes and the messages have not caught up yet. The record remembers the work even when the week felt quiet.
A caution. Do not let the tally become the point. A tick is a reminder, not a trophy, and a post made only to keep the run going, with nothing real in it, is worse than an honest gap. Count posts that were actually worth seeing, not filler put up to protect a streak. Keep it to a simple yes or no on whether you showed up; do not turn it into a wall of numbers to chase.
The short version: you keep going when you can see you are getting somewhere. Keep a simple, visible tally of the posts you have actually made, one tick each, somewhere you pass every day. Do not chase a streak for its own sake. Just let the growing row remind you that you are doing the thing, and make the next tick the easy one to add.
Print the free A4 calendar and use it as your tally: a tick on every day you post. After a few weeks the row of ticks is there every time you pass it, quietly telling you to keep the run going.