Pregnancy Test 🤷🏻‍♀️

Would a positive show up 18 days after sex on a $1 test? I’m on a budget and the only red dye tests around me are the cassette $1 ones. The $5 ones are blue, and I hear a lot of false positives/dye runs from them.

Edit: I don’t know if I ovulate. I’m on BC and my last withdrawal bleed was 8/28.