I need some advice.

Now my last monthly was on january 31st. I am on a 40 day cycle. My boyfriend and I had unprotected sex on the 25th and 26th of february.
On march 2nd I started bleeding a very light red color for 3 days only. Then on sunday I started spotting brown blood it look like nothing worth wearing a sanitary napkin for and it only lasted a few hours. My monthly isn't due until the 12th. I took a hpt on the wed the 9th and got a negative response. Is there a way that I could be pregnant and just took the hpt too early.