Positive & negative testing???

Has anyone on here tested positive 3 weeks after conception but also had negative tests too? I tested positive with my pee that was held all day. Once I seen it was positive I drank water to pee again and took another one 30 minutes later and it was negative. I’m going to take another one in the morning but I was just wondering if any of you have experienced this.. I still have a week and a half until my period is due. I know I would be very very early. TIA!!