What makes sex make me feel like i need to go toilet?

Normal : This is completely normal and happens in both men and women. Intense feelings during sex and ejaculation/orgasm can make severe muscles around the genitalia contract in unison, some of which that are involved in contracting to pass urine. Also passing urine after ejaculation in men is the body' way of flushing the urethra of the reproductive fluids.

Cystitis: There can be trauma post sex or urine infection which can increase urge to pee more. Can try lubricant , if symptoms persist then maybe urine test and discussing with your doctor.