Weird cycle or implantation?

So, I just started using this app to track my cycles just recently (1/22). I have PCOS and my cycles are crazy irregular. I started taking Metformin in Sept 2015 and by November I had a period! (The last one was April and before that Jan.)  I had a period start on 12/31/15 and end 1/5/16. Pretty normal for me. 

Fast forward to last week. My SO and I were having sex Tuesday night. When we finished, he noticed I was bleeding. It wasn't a lot, but I was confused bc I usually have a day of spotting before it actually starts. (& I wasn't expected to start for atleast another 2-3 weeks) So the next day I noticed my period was super light and basically on the line of spotting and light. And up until Saturday, it was just spotting.  We had sex on 1/23, and honestly I don't know how many times we had sex between my last period and then (maybe 2 times?). 

Could this be implantation bleeding? I just wanted to get some opinions before I decide to test. 

Thanks!