Faint line 12 hours later??

I took a pregnancy test last night (randomly bc my cycle this month was strange) and got a BFN. This morning I checked the same test strip again out of the trash and there is a faint line. It is a wondfu test strip. 
​Should I just disregard the 12 hr old test? 
​My breasts are sore but that is common for me when AF is coming. I've had pain in my lower right pelvis for 3 days... Not sure what that's about. Also I keep getting headaches but that's kind of typical for me.