welcome to healthcare magi forum
thank you for your query
i understand your concern about bruise
due to pressure and friction you have develop bruise on butt.
you may feel up to 3-4 days.
apply good antibiotic cream over it
it is better to take analgesic
medicine for pain and inflammation .
it will turn into brown and than black.
if you feel more swelling ,more pain ,it better to consult doctor
i hope i answered your query