My Birth Control Shot Has Made Me Feel Really Weird

My birth control shot has made me feel really weird lately and I'm having side effects that I'm not used to with it.
Not to get all gross and all, but the shot is supposed to stop your period and all. I've had spotting before but it was always really super light or like old blood and brown in color. Now it's super red and slightly heavier bleeding. I just had a few clumps of blood when I wiped after peeing. It feels like I have cramps now, which never happened and my lower back is killing me. I took a home pregnancy test and it was negative. Im just super nervous.
I'm just scared they're going to tell me something is wrong. :/ what do you think?