hpt BFP but negative blood test??

I have irregular cycles and currently on CD53. I know i ovulated on March 3rd and implanted on the 11th ao i would be 5w5days today. so I'm 25dpo today and took a First Response hpt with FMU and it was positive! I sent a message to my doctor and had my blood tested a few hours later but came back negative. is it just too early for the blood tests to show? I'm leaving tomorrow on vacation to Vegas and want to make sure I don't give my hopes up. She said it's possible I'm pregnant but might be too early to show on a blood test. Has this happened to anyone else and they tested over the next few days with BFP then later got a positive blood test? TIA