Birth control and sex

I'm not sure if this is the right topic to post in. But I've been on the Depo injection for just under a month now, before this I never bled during or after sex. I had sex a week after having the Depo (recommended by doctor) and i was fine, but after that first time, every time I've had sex, I've either bled a lot of browny red or a little bit of bright red. I'm not sure if this is normal or not.. Any advice???