Help - I need some advice!!

I am around 12 DPO and am pretty sure I experienced implantation bleeding about four days ago (am still getting very tiny amount of reddish brown CM), but I did an ultra sensitive Fortel HPT this morning and it come back a BFN. However, I also did a OPK and it come back ++. Not as dark as the control line but a definite line. I also have had sore BB's for the past week and have been feeling nausea's for the past couple of days and experiencing strange cramps.

Do you think that I should just wait a couple of days and repeat another ultra sensitive test - do you think it is safe to say that I may have a little person forming? Talk about anxious!

Let me know your thoughts?