Muscular Endurance?

whenever i hit the mitts or bgs i can go pretty hard and hit pretty hard for a couple rounds but then i lose almost all my power and am hitting like a total fucking pussy. is this just my muscular endurance sucks right now or what? I am very strong especially for my size but I lose my power pretty quick and my arms become jello.

ttt

learn to pace yourself too and try to shorten your
punches.

Roadwork and sparring will increase endurance. Keep training and give yourself time...and remember to breathe!

Is a press-up just a push up from handstand position?

Press up = regular push up in UK-speak.