Brown blood is old blood. Some periods are just absolutely strange. Some will have clots/tissue, others will not. Some will be light and some will flow like a river. Sounds like your hormones just got out of whack this past cycle and your period is messed up. I'd count the spotting as your period.
Yes. I did. and I spotted throughout when i should have had a period then it stopped.
Did you have unprotected sex? Usually spotting isn't a sign a pregnancy. Implantation bleeding is about 7-10 days before your missed period and is light pink. Try taking another pregnancy test in a week if still negative and no period contact your doctor and request a blood test.