Wow sex is gud lol.. but i got a sorta question..

when i put it on its practically normal i think, but then because of the comotion i get a little turned of and a little flacid kinda quick, but after arousual the condom has mishapened, often its stretches to far and sometiems during intercourse when i pull it out, its about 1/2 inches to extended. i dont know if its because i put it on wrong, or wether its cos my penis is too small or big but its this normal?