I heard from somewhere (don't know where, so don't know how accurate) that brown blood is okay because it's old blood. The bright red is new blood, but I know that my sister had what she thought was a normal (maybe light) period when she was due for it after she got pregnant, so she didn't even know she was pregnant until she was 8 or 9 weeks along. So, she had red blood, and her daughter is now 2 years old. I agree that you should ask for an u/s, but I wouldn't get one until 6 1/2 to 7 weeks because you might not be able to see a hb before that, and that would scare me to not see one. Good luck!
Its possible. I spotted during one pregnancy and went on to have a miscarriage and during this one I bled like a period for 5 weeks and everything turned out fine. I would ask your doctor to get you an early ultrasound (6-8 weeks) to see if everything is okay in there.