Increase My Stamina?

Was and still my maybe problem, I get tired really fast. How can I increase my stamina? Some players in my gym say don’t run for long miles or your body will lose muscle an stuff like that, others say stick with sprints. I do MMA and training MMA in the Gym is not enough to make my stamina good since I do train for 2 or 3 days at the moment. I also found out that sex 3 or 2 times a week would make the stamina even worse for the nest days of training.

I have strength and flexibility, all I need is to get tired after 15 min or more, but what’s the right way to do it?

Sorry for bad english it’s my 2nd language.
I weight 78, Hight 173 and I’m 20

What people are telling you are right. Don’t run for long miles and stick to sprinting HIIT style.

With Tabata thrusters, it will only take 4 minutes to tire you out.