Soon after having sex, always go and have a pee . It is preferable to have a wash straight away, but if you are too tired to do this, wash when you get up in the morning.
It may be that you have an allergy to the latex, so get your boyfriend to try the latex free condoms. Do not use soaps, bath or shower gels to wash below, normal water is fine. Using a soap with the same pH level as our skin is fine and baby washes may be fine.