When i'm crouching for a few minutes my legs start burning. normal?

I'm a 34 yold male. I'm currently hammering pavement to change tiles. So when I'm crouching for a few minutes my legs start burning, I feel tired and if I don't stand up immediately I'll start feeling dizzy. Afterwards my legs will be aching for hours and I get overall really tired.

It's been like this my whole life except when I was a child. When I squatted in the gym I could do few reps and very little weights and right after I would lie down for some 10-20m sweating exhausted. In the inclined squatting machine I didn't have no problem hitting the max load for several sets. Also I can do 30km (18miles) a day in bike no problem. But I get totally blown if I sprint with my legs for 2m.

I'm a little over weight with some 110kgs (243lbs) and 1.80m (5ft 11in) in height, although quite muscular with very little belly, meso to endomorphic body type (think of a small American football player).

It doesn't matter how much an active or sedentary life I'm currently doing. It will just happen.

So, I guess this doesn't really happen to skinny people, but what about overweight people? Is this normal?