

Carrying or working with the weight always on one side quietly pulls your back out of balance. A tool bag over the same shoulder, a load hoisted onto one hip, feeding a job from the same side all day, it all means your back works harder on one side to keep you upright. Sharing the load out is what settles it down.
Your back is happiest carrying weight evenly, balanced over your middle. Load one side and your back muscles on the other side have to work constantly to stop you tipping over, holding you upright against the pull. That ongoing, lopsided effort is what tires and aches, often on one side more than the other. It is not a sign of weakness, just the natural result of your back countering an off-centre load for hours. Even it up and the strain eases.
If you cannot avoid carrying on one side, the next best thing is to keep swapping. Changing which shoulder or hip takes the load, or which hand does the carrying, means neither side is under strain the whole time. It feels odd to use your weaker side at first, but it shares the work and keeps you more even. Making a habit of switching, at natural breaks in the task, stops one side quietly taking everything shift after shift.
Sometimes the fix is in how the load is carried rather than which side. Splitting a load into two, one in each hand, keeps you centred and upright far better than one heavy weight on one side. A rucksack or a proper carrying frame spreads weight across both shoulders and your back rather than dragging you to one side. Where a load has to sit on one side, keeping it as close to your body as possible reduces how hard your back has to pull against it.
One-sided work often comes with twisting, reaching across to one side with a weight, or turning to place a load while your feet stay put. Twisting with a load on board is where the back is most easily caught out. Turning by stepping your feet round, so your whole body moves together, keeps your spine safe. Setting things up so the load does not have to travel across your body, and you can face where it is going, takes the twist out of the job.
If your back feels it, often on one side, after a day of uneven loading, gentle movement usually helps it settle. A short walk, easing your back gently the opposite way to how it was loaded, or a little warmth often take the edge off. Staying gently active tends to help more than stiffening up. What works varies from person to person, so it is worth seeing what settles yours.
If you would like to try a guided back stretch, VIDA has a short video you can follow at your own pace.