Male, 80-90 kg, 5 feet 10 inches.
For my entire adult life I have been getting tired in my lower back if I spend an hour walking around at the mall.
Once I participated in a canoeing course and after a couple of hours in the canoe, my lower back hurt so much that I almost passed out (It was also really sunny).
If I do 4 sets of 10-15 back extensions then my lower back feels really exhausted. This feeling is different from when I do pullups or bench presses or squats. In the latter cases I do not really feel exhaustion in the same way and at most I merely feel like I lack the strength to perform more repetitions.
There seems to be a correlation between me doing deadlifts and catching a cold, and my lower back typically is the body part that feels the most drained afterwards, so I tend to avoid doing that exercise. This might be nonsense though.
A year ago I injured my lower back doing a seated low cable row. This was during warm-up so the weights weren't near my maximum capacity. This left me walking like a T-rex for a couple of weeks. Then a couple of months later I went on a day hike, and my back felt fine, but the day after, when I bent to pick up my shoes, pain suddenly shot through my lower back, and I ended up walking like a T-rex for a couple of more weeks.
Recently I was doing a plank and I typically do 4 minutes. After 2 minutes something felt wrong about my posture, so I stopped doing it. Later that day I did some simple squats (no weights) and I ended up injuring my back again. I recently switched apartments and the bed in this apartment is smaller and feels softer, so that could be related.
What could be reasons that my lower back gets tired quickly, and how can I work out to strengthen it?