last few periods only last three days?

Hi,
Welcome to ehealthforum,
Dark menstrual bleeding could indicate chances of hormonal changes, infections, endometritis, ovarian cysts, use of any medications, etc. The exact cause can only be made out after careful evaluation. Consider visiting your doctor/gynecologist at the earliest for thorough examination and further evaluation to look for the underlying cause for the abnormal bleeding that you describe. Treatment as needed (based on examination findings and investigations results) would be started to help you control the bleeding and regulate your periods. Consider being in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Drink plenty of water. Take adequate rest. Maintain healthy diet and lifestyle.
Take care.