Worried that the Depo Shot isn't working

I'm on the shot right now. When I first got it, I had sex about a month with my boyfriend after I got it and nothing happened. I just got another one in January. Well me and my boyfriend had sex a couple of days after Valentine's day because we took a break, and I started bleeding. I thought it was nothing until we had sex again this past Friday and I was bleeding again. It was like spotting. But this morning I woke up and I felt wet and I haven't had a period since I first got the shot. I had a bit of blood like a light flow. Is it normal? Could I get pregnant? I don't get another shot until April. If I didn't explain it right, im sorry, I have trouble with English.