Last sexual encounter was 7wks ago, period was 3wks after only heavy for 1 day, took a hpt 4wks after (neg). brown spotting today could i be pregnant?

When in doubt: just check another pregnancy test 1 week after last negative one. And if you are still not bleeding normally and first pregnancy test was negative, check it again in 1 week. But it is not likely that you are pregnant given the normal period initiation. Your hormones are perhaps in flux and will likely self-regulate if given enough time. Or you may need to visit a healthcare professional to help

Pregnancy: You have had a normally time period 4week ago and bleeding now and a negative pregnancy test. The likelihood of pregnancy is exceedingly low.