15 days but no darker hpt?

I've been getting vvfls for 15 days now but they aren't darkening at all. On the 3rd my blood test showed only 1hcg so I have no idea if it's the tests, or my body, or what's going on but does anyone have a similar experience? My period hasn't started but I don't know when it should, I'm cramping, and I'm having crazy cm (sorry tmi), fml.