My best friend took ten at home pregnancy tests that her mom brought home from her work, she's a nurse. All were negative. But she knew her period was missed so went in for a blood test and sure enough she was pregnant. It could just be your hormine levels aren't high enough to detect yet in a home test. Good luck!
Your doctor likely said that because there is no point in doing testing like ultrasounds until slightly later on in the pregnancy. (because you don't see much until 6, sometimes 7 weeks) One thing I will ask though, is are you using your morning urine to test? Because you're most likely to get a positive test when your urine is more concentrated, and not diluted from drinking liquids all day. My best advice to you would be to take a different brand of hpt in a few days. If that turns out negative, wait a week and try again. But its completely possible that you just want this so bad your brain is tricking your body to believing it is, theres just no hormones there. Good luck hun, I hope you can get an answer soon:)