Hello. Thank you for writing.
At your age, period irregularity is not uncommon as you are still maturing. Stress can also contribute to the delay.
Pre-ejaculate fluid in itself does not contain sperm. Sperm can be picked up the urethra if a man has not urinated since ejaculation. But once he urinates, any sperm would be flushed out.
You can't get pregnant from a swimming pool. Sperm ejaculated outside the human body don't live long. Seminal fluid dries out very quickly when outside the human body, once it is dried the sperm die almost immediately. Dissipated into pool water, a similar outcome would occur. Life of sperm increases once ejaculated inside the female body and can actually live a few days in a fallopian tube waiting for an egg. Outside the body, they're doomed!