23 year old here, second time ever having sex. First time was with a hooker about a month ago.

See the first time it was nice as I didn't finish in 1 minute. However after 25 minutes when I am about to come I reflexively, for lack of a better word" flex my pc muscles delaying ejaculation.

Once this happens I gradually lose my erection. It was dissapointing since in general I was better than last time and even got the the thrusting right.

Girl was not a pro and was attractive to me. Any thoughts/advice?