Could the reason be why the pregnancy test were negative because they where from dollar tree?

No: No, the source of the pregnancy test should have no bearing on how accurate it is.

I suppose: It's probably more likely that your urinary levels of HCG were not yet elevated enough to be detected. The over-the-counter tests aren't always as sensitive as tests at your doctor's office, but even those usually take several days after you're late to turn positive. Best to recheck 1-2 wks later if you're late for your period & suspect you might be pregnant. In any case-congratulations!