Has this happened to anyone else??

Crystal
This past Saturday night, I took a clear blue digital w/ week predictor test - BFP! Woke up Sunday morning took same type of test and got a BFN! Waited a day, then Yesterday afternoon took same type of test, BFP! Woke up this morning took another and a BFN! :( this is worrying me and has me so confused, has anyone else only recieved positive results in the afternoon or at night only?  Every time I've tested my first urine I've gotten negatives! I'm 24 DPO and feel like by now I should definitely be getting consistent positives. I have a Dr. Appt Friday but I'm worried