Hello sir I m 22yrs old.

whn i sex 2nd or 3rd time wth my gf my penis get small n it take atleast  1 hr to get erect why this is happening is it normal n we do sex 2times in mnth n evn 2nd time I can’t last longer avg is 3min 2nd time plzz hlp I wnt 2 give her orgasm.

any tips n shuld I go to dr plzzz rply me