I've Been On The Depo Shot For About A Year

I've been on the depo shot for about a year now and have always had irregular periods. I'm due for my next shot this week. I had unprotected sex twice last weekend and the weekend before. The first time my boyfriend ejactulated in me and nothing happened. This last weekend, he did it again and I started bleeding afterwards. It's been a week and I am still spotting brown and light bleeding. Am I pregnant? Should I be overly concerned?