In the context of pushing a pebble, work is defined as the force exerted on the pebble that causes it to be displaced over a distance.
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When you push a pebble lying on a surface, the pebble moves through a distance. You exert a force on the pebble, causing it to be displaced. In this situation, work is done.
The scientific definition of work requires a force causing a displacement, whereas the everyday understanding of work involves any physical effort or energy expenditure, regardless of whether there is displacement.
No work is done on the load when you stand still with it on your head because there is no displacement of the load in the direction of the force you are applying.
Standing still for a few minutes with a heavy load on your head results in tiredness and expenditure of energy, but no work is done on the load according to the scientific definition.