OMG Michelle, not necessarily..... UM, FRER!!!!!
Picture please! If the line showed up in the time frame sounds like a real line to me. We need details...what type of test? The line could very likely still be light at 13 DPO. I was looking back at some of my test and I have an IC from 13 DPO with a really light line when I was pregnant.
I agree with the PPs, we need more info!!!!!
It could still be very light at 13 DPO. Remember, some people don't get a positive at all until after AF is due. If implantation can occur as late as 10 DPO then you could still have a very faint amount of HCG, in theory. Plus, some tests do not pick up anything under 50-100 mIU/mL