How to build endurance? I have none now. :(. ?

Umm, have you gone to a doctor? Maybe you have asthma, and you just don't know? That's maybe my guess. But also, you may not know, (but you may also) but once you run or walk, don't sit down right after. It's not good to do that after a run. But don't get discouraged! You're doing a great thing by staying fit :)