Good way to build stamina quickly?

have you tried HIIT? if not you should definitely look into it. i know when i come off bulks. out of shape, i cant run 2 feet. HIIT just seems so much easier at that point. as for stamina. that will come with time really.

When it comes to running there's really only two types you should focus on : speed training and endurance training .

Speed training works by picking a set distance and aiming to beat your times . I do a 5k run and my current record is 24 mins. Speed training helps condition your muscles to withstand that exercise.

Endurance training works by simply running as far as possible without focusing on your speed. My current record is 9ks.
Endurance training builds muscles and increases your stamina .

In alternating between the two you'll see gradual and consistent improvement. I run one speed training session once a week every Wednesday and one endurance training session once every two weeks on the Sunday.

There's mechanics behind it that focus on your body's slow-twitch and fast-twitch muscles. Martial artists do this type of training in their katas and sparring sessions respectively.