spotting or weird period?!

Hello ladies! First time poster here 😊 so I'll get straight to it. I have been "bleeding" for 10 days...this is new to me and I'm 26 years old🙄( I thought I had this crap figured out) so some back story...had my first child a year ago, stopped breastfeeding at 3 months, went on the shot (same bc I was on prebaby, no issues) last shot was Sept 2016, had some normal periods between then and now, so now what I have I don't even know if it counts as a period. My flow has been super light the whole time, no cramping, no clots, nothing like my normal "oh my God the red tide is upon me!!!" I've been more moody and irritable, but that's the only "normal" side effect.  So basically my question is WTF is the difference between a light period flow, spotting, and implantation bleeding?? I've considered calling my doctor but don't want to be freaking out over nothing. 😫 thanks in advance ladies!!