Correct time to uze Pregnancy Test Kit

Hello. I would like to ask if Preganancy test kit will work 5days after concepcion? We tried did a PT around a week after we made love but PT results were negative (Thinking it would be detected immediately days afyer concepcion). We tried it again 2days after scheduled menstration and it showed Positive! (yay) any chance it gave us the wrong result? Is Blood Chem more accurate way to do PT? Thanks!