You should perform ghusl after 8 days-it it the pattern of your monthly cycle before this condition. The bleeding past the eight days, in your case, will not be considered as due to menses; rather it is reckoned as istihadhah; in the case of istihadhah you perform salah and fast as you would do after having performed ghusl at the expiry of menses; you need to wash your private parts prior to each salah as close to it as possible.
For details, please consult the following answers.