clear blue test question

I took a test with the clear blue digital, said not pregnant. I opened it up just cause I was curious and saw a second faint line. I opened a none used one to see if it's always there, which it's not. I haven't gotten my period back from since I stopped breastfeeding 7 weeks ago so just testing because I feel pregnant. I've heard stuff about blue dye being bad. I used first response with my first pregnancy and got a dark, clear positive.