Keep chemically straightened hair straight?

got hair done a week ago. it's already back to bein an afro. i took a shower later that day i got it done, which i now know is bad + its so humid wear i live so now its really frizzy and you can't even tell i got it done. so how long should i wait next time i straighten it. and what are some at home products to restraighten hair, god forbid these people at the store told me if i mix wrong chems my hair could fall out!! haha. thanks