Hi,
Welcome to ehealthforum,
The spotting that you describe could also be attributed to the hormonal contraceptive injection. If it is persistent, you should consider visiting your doctor/gynecologist for further evaluation to look for underlying cause (hormonal imbalance, endometrial problems/hyperplasia, endometritis, ovarian cysts, anemia, bleeding disorders, etc). Treatment as appropriate (based on examination findings and investigations results) would be started to help you regulate your periods. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Take adequate rest. Drink plenty of water. Maintain healthy diet and lifestyle.
Take care.