12 DPO, negative pregnancy test but darkening OPK??

So I posted yesterday stating I didn't know that there is an LH surge during pregnancy and someone comfirmed for me that this is true. I just took a pregnancy test and got a BFN but my opk is getting darker as the days go on (a lot darker than yesterday's). Does this even mean anything? I am 12ish DPO and have AF cramps but have been cramping probably since ovulation. Once again, I am aware that waiting is the only option obviously but some input from someone that is more knowledgeable about this than I am would be helpful. :)