Depo Shot

So I don’t know if this is really the group to post this on, but I have some questions about the shot. I have a “normal”period once every 3

Months with the shot But after I have the period midway through the second month I start spotting like crazy?? I don’t understand. It makes me feel awful like I’m on my period but it’s just spotting. Also with this shot I’ve gained over 50 pounds in a year...I feel like I might should switch birth controls. Maybe the bar in my arm? But I am TERRIFIED of that thing getting put in my arm. Please help!