I just don't understand...

So I'm currently a week late. I have had faint positives on home pregnancy tests but when I went to the doctors to confirm they said I had no hcg in my blood test.... I'm usually never late.. I don't know if I'll having a chemical, lost it, or was not pregnant - but if I wasn't why am I having faint tests?? I just don't understand what's happening... can someone help me?