Depo Period?

So I've been on the shot for 3 months and haven't had any bleeding or spotting at all and everything has been great. I am due for my next shot next week but I ended up getting sick and am now on antibiotics so I want to finish my 10 day treatment before I get the shot because I've heard too many stories about antibiotics making birth control fail. However the last 5 days I've had some brown spotting and today I'm cramping and having pink bleeding?? I don't think I could be pregnant because he's never came inside me and I'm on the depo shot. Am I bleeding and cramping because I'm due for my next shot or is my body still adjusting? Is it bc of the antibiotics?