Just how heavy is your laptop?
You need a better backpack I think? I regularly carry 10kg of groceries in my backpack over two kilometers. It never gave me any back pain.
Carrying a heavy backpack can be practiced. It does not hurt your back.
People complain they can't lift shit but don't do anything besides taking anti pain pill.
The secret to growing well is avoiding processed food, cardio 30 min per day minimum and weight lifting.
I do use an Osprey 22L hiking backpack for my daily driver, it's got a waist belt to transfer weight to my hips, a chest strap to keep the shoulder straps together, and internal semi-rigid frame... but that's more for all my other stuff, and for activities I do in the woods far from stuff like 'laptop computers'. Even if it's just in a handheld briefcase, 3 kg is not a lot. That's about as much as a water bottle - which I also have in the backpack, as well as a bunch of miscellaneous stuff that also weighs a few kg.
I herniated a disk a couple years ago due to a waterskiing accident, but I've fully recovered and even while dealing with that injury, walking around airports and so forth with any laptop is not not strenuous.
In hindsight, I wish I'd gone for the big P73, I miss the giant 17" screen of my old 40mm thick, 3.5 kg Dell Precision... but the OLED on the P53 is beautiful. 17" UHD OLED when, Lenovo?