Negative test turned positive after a few hours

Okay so like, help me guys. I do NOT want to have another baby. I just gave birth 8 weeks ago and I have been so so careful. I’m 12 days late for my period and I decided to take a test even tho I figured it’d be negative, because I’ve been careful. And then a few hours later it had a faint faint line. And I’ve been freaking out since. The line disappears though when held to a light bulb!? Opinions??? Also I’ve been cramping for like a week thinking my periods coming but then have been having brown watery discharge