Well, you're gettin' pretty late with your period, so that of course is a distinct sign that you could be pregnant, but that lower abdominal pain sounds strange to me. Have you ever been pregnant before? If you have, are the pains usual for you?
I would a) get a better quality test and try again, b)see your doctor about a blood test if you don't want to buy another test or it still comes out negative and then finally, consider asking for an ultrasound if the pain continues, whether or not you find out if you're pregnant.
I don't want to scare you, but I was just reading about tubal pregnancies the other day, and pregnancy hormones are often lower with them--so that hpt's often don't respond. The pain you're having
be a bad sign. Ultrasound could tell.
Good luck! Let us know how it turns out!