kinda scared

So I started the depo shot in January 26 of this year. In February I didn't have a period but this month I guess I started? Like I bled on the fourth so I put in a tampon went to sleep woke up and took it out and there wasn't anything but like what happens at the end of your period the dark brown stuff so I carried on with my day later in I felt something "down there" and went and checked and I was bleeding again so another tampon just went and changed it and it was the same thing the dark brown stuff !! My stomach is killing me all around and idk what to do? Is this normal?