Faint positive?

I took this test yesterday morning, and got a faint positive, but today tested with a new test and got a BFN. I'm only 6-7DPO and twins run in the family. Not sure if I should be discouraged yet or if one test was stronger than the other, or one FMU was less diluted than the other. I got a positive on ClearBlue Plus and a negative on ​​​