At home pregnancy test after 8 weeks? Help I don't see a doctor until next week.

Kadie • :)
I had a light period my last one and I still haven't started yet. I was told I could be pregnant because a few of mine has been faint positives. But now I'm getting a negative. Is it true after 6-8 weeks of pregnancy the at home test won't work right? I would have gotten pregnant the 18th of January