Negative test at 12 dpo

Jessenia

Af is expected to come in 2 days I took a clear blue digital test today and it was negative. I have had cramps for two days, watery mucus and very dizzy, tired and nauseas and also some lower back pain. Should I wait to test again after my missed period? When is the best time to test ? I was told 14-16 dpo is the best time to take a test is this true ?