It happened to me. I had a pos hpt at 9dpo and went to the dr the same day, because I am high risk. They did a urine test and a blood test and both came back negative. He told me we always have next month, this was just the first month using Clomid and not to get down. I was convinced I was pregnant, so I just kept testing at home and sure enough I am pregnant. It was just too early to show up on the blood test since I was only 9dpo.
So you know how many dpo you are?