Possibly Pregnant?? Implantation Bleeding???

Okay so I got my Mirena out on the 31st and started my period 2 days later on the 2nd and it ended on the 6th. Now it's been 5 days later and I have been cramping today and when I went to the bathroom there was a little bit of brown spotting. Now we are not trying to get pregnant but if it happens then it happens. Also we have been doing the withdrawal method. I know it might be way to early but I haven't had normal cycles due to the mirena so I don't know my cycle length. Also I wasn't on it for the full 5 years. I was only on it for 1.