Menstrual blood may be dark red when you get up after being seated for a long time. Or, it may be a sign of implantation. After delivery, you may experience heavy bleeding with dark red or black clots. Foreign objects like tampons stuck in your vagina can cause black discharge. In any case, consult your doctor if you see something unusual.
Mid-cycle bleeding or spotting is a result of thickened endometrium during ovulation. Estrogen levels dip, and progesterone rises temporarily to support the endometrium. Insufficient levels of progesterone may cause spotting, which lasts from 1-3 days. Other reasons for spotting may be hormonal changes, PCOS (Polycystic Ovarian Syndrome), or pregnancy.
Prostaglandins are the chemicals that cause your uterus to contract to facilitate the uterine lining expulsion. It causes period pain called dysmenorrhea. Period pain that started when you are younger may lessen with age or after childbirth. However, secondary dysmenorrhea that begins later in life may be due to conditions like endometriosis and fibroids.