When Moesha goes to get the birth control pills, she does eventually get them. I don't recall her mentioning receiving any condoms. As soon as she get the pills, she gets ready to have sex with Aaron. There would have still been a chance that she would have gotten pregnant, because pills don't work overnight. They don't protect from STD's either.
EDIT: When Dee talks to Moesha, Moesha tells her that she's been taking the pills for two weeks, which is long enough for the pills to work to avoid pregnancy.