I'm guessing this is a chemical? Any advice?

I did a first response test last Saturday (12 dpo) and got a positive. Faint but easy enough to see.

I've had quite a few symptoms. Tested this morning with the same test and no line at all! So I guess it just means I was but now I'm not.

What I'm finding weird is that I still had symptoms yesterday and this morning. .. migraine last night, shaky and nausea when I woke up plus very strong sense of smell. Period due yesterday and no sign yet.

Oh I'm fairly sure I implanted on 6 dpo too.