Depo shot

So I’ve been on the depo shot for a month now. My partner &’ I have been using condoms still until yesterday that he used the pull out method. That was the first time we had done it without condoms. Today I woke up with a light spotting & I was wondering why that might be. Is it one of the symptoms for depo? Or ?? I’ve been trying to look for it online but I can’t find answers. I haven’t had my period in 25 days