Faint Blue Line

I got my Mirena removed 1 month ago and immediately started trying to conceive. I took a test the day before my period started and it said negative. I started my period a week ago today and it was a normal cycle and today I wake up and am still spotting. I have been tremendously moody the last few days so I woke up today and took a test and it has a faint positive line?! How can it be when I’m on my period? Anyone else have this problem?!