Why does my period lasts a month sometimes?is that normal?

Not normal: Having a period that lasts longer than one week is not normal. See your gynecologist for a history and examination. Prolonged menstrual blood loss can cause anemia (low blood counts) and the causes are varied, from dysfunctional uterine bleeding, fibroids, endometriosis, and others.

See Gyn Soon: Abnormal periods need evaluation; sonogram, lab tests. Non-surgical options include: birth control pills. Lysteda (non-hormonal rx taken during period), Mirena (levonorgestrel) iud. Minimally invasive options: endometrial ablation (in-office), hysteroscopy polyp removal or fibroid resection; and only if these treatments fail then consider hysterectomy - vaginal or laparoscopic if possible.

Not normal: After ruling out pregnancy (ectopic), you deserve an endocrine and perhaps a hematological evaluation to rule out medical causes such as hypothyroidism, pcos, and coagulation defects. If you have been skipping cycles on the past (which is also not normal if pass the age of menarche by a year), then you could have a problem with ovulation which can give a similar problem to what your experiencing.