you have history of breast cancer
, possibly must have undergone adjuant chemotherapy
following which you had pregnancy so you must have developed two way amenorrhoea, one chemotherapy induced and second lactational.
Basically you are a young lady with active hormonal status. Once the menstrual suppressant factors waned you have started with fresh bleeding.S ince there must not have been a good passage to the menstrual flow it landed into clot formation. After one or two cycles of this clotted menstrual flow you should have normal flow with certain supportive medications to be prescribed by your doctor.
I don't know what was your hormonal status after breast surgery
. Normally at this age of yours breast cancers are aggressive because of the active hormonal status. You may need to undergo artificial menopause
so that there is no recurrence of cancer or or there is no new cancer formation.
Please seek the advice of a good clinical Oncologist
who should guide you the future best course of action.