Thanks for the query.
Depo can cause side effects like pain abdomen, breakthrough bleeding
So possibly the bleeding could the side effect of the depo.
If the same thing gets repeated, you once consult gynecologist get examined to rule out the possibilities like pelvic inflammatory disease
Then you can go for symptomatic treatment in future if needed.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429