Meaning to post is not the same as posting. The shops that keep it up are not more disciplined than you; they have simply decided, in advance, exactly when they will do it. That one decision is most of the battle.
There is strong evidence for this. People who decide ahead of time precisely when and where they will do something follow through far more often than people who only intend to. A review of ninety-four studies found the effect medium to large (Gollwitzer and Sheeran 2006, a meta-analysis of 94 studies). “I’ll post more” fails. “I’ll post every Tuesday morning while the kettle boils” works, because the decision is already made when the moment comes.
Halloween shows the small version of this. The businesses that manage two good posts in the run-up are the ones who put those two posts in the diary weeks before, each with a day and a time. You can see this on the Halloween run-up: deciding the day now is most of what gets the post actually made.
So do the deciding once, when you are calm, not every day when you are busy. Pick your slot. A day and a time you can realistically keep. “Tuesday, first thing.” “Friday, after the lunch rush.” Tie it to something you already do so it has an anchor: while the coffee brews, before you cash up, after you drop the kids. The anchor is what turns a good intention into an actual habit. A barber might tie it to the first quiet gap on a Tuesday; a baker to the moment the first batch is out and cooling. The point is that the moment already exists in your day, so you are adding one small thing to a slot you were going to be in anyway, not carving out fresh time you do not have.
Then write it down where you will see it. A plan in your head is easy to skip. A plan on the wall is a small nudge every time you pass it. Put your posting day on a calendar you actually look at, in the shop, by the till, on the fridge, and the decision keeps reminding you of itself.
This also removes the daily argument with yourself. If posting is an open question every morning, you will lose that argument on the busy days, which are most of them. If the day and time are already fixed, there is nothing to decide, only something to do. You have taken willpower out of it, which is the point, because willpower is exactly what runs short when the shop is full.
A caution. Be honest about the slot you can keep, not the one you wish you could. Once a week that actually happens beats three times a week that collapses after a fortnight. Pick a rhythm that survives a bad week, and only add to it once the first slot is second nature. A plan you can keep is worth ten you cannot.
The short version: do not rely on remembering or on feeling like it. Decide now, once, the exact day and time you will post, anchor it to something you already do, and write it where you will see it. The shops that keep going are not tougher than you; they just made the decision in advance, so on the day there is nothing left to decide.
Print the free A4 calendar, mark your posting day on it, and hang it where you work. With the day fixed on the wall, there is nothing left to decide each morning, only something to do.