pregnant?

I am 4 months post partum and had an IUD placed 2 months ago. It's the copper one. I have had two friends get prego with it in and caused one of them to miscarry so I've scheduled to get it removed later this month. So after my IUD was first placed I bled for a few days and then  completely stopped. I still have not gotten my period back since I'm breastfeeding. Well two days ago I lightly spotted and ever since then I've been in the mood to do the deed. Lol! Then it occurred that maybe it could be implantation bleeding and that's why I've been in the mood lately?! When could I test and it would show a positive? I'm probably over thinking stuff but I'm worried.