15dpo, 1period 1 day late

As the title says I'm currently 15dpo and my period is 1 day late (due yesterday). I had lower back ache at 9/10dpo which turned into cramping at 12/13dpo. Then no more cramping just sore boobs and a lot of nausea and headaches. I took a test 12dpo and BFN. I had some really really faint pink spotting yesterday and then again today just when I wiped, but now I'm having sharp pain, maybe gas/wind? I have the worst constipation as well as a head cold! Thinking of testing again at 18dpo. Thoughts?