I am having the same issue. I got a positive and like you I wanted to be sure so I retook the test and got a negative 3 times. I was due on the 23rd but nothing.
go to www.peeonastick.com
Someone here mentioned it before. It is a funny, informative, and useful site, despite the name. Lots and lots of very good info about anything to do with HPTs.
Get a two-pack take one with first morning urine, would should have higher concentration of HCG. If that's negative, wait a week, and if still no period, take the second one with first morning urine. If still negative, go to doc. They can order a blood test, which is more accurate. Also depends how late you are too, as to how well the tests work. God bless and let us know what happens!