clear blue digital test?

Okay, so when I found out I was pregnant I got a box of three clear blue digital tests, I took one that day it said pregnant 1-2 weeks. I had a ton of cheep test from eBay I took everyday to detect my hcg levels. All test were darker each day, and seamed normal. It's been a few weeks at this point I am almost 8 weeks. Yesterday I took my last cheap test and it was a dark strong positive. Today I took one of the digital test and it said not pregnant.. But the weeks estimated line said 3+ weeks, also the waiting symbol never went away? Is it a test error? Or is something wrong with the baby?? I'm so worried..