Congratulations! I think many of the women on the Pregnancy forum have experienced brown spotting. From what I understand, it is most often old blood and not of concern. It should stop soon.
As for the ultrasound, I haven't had one yet and I will be 6 weeks tomorrow. As much as I'd love to see my little one ~ I'd rather see that it was healthy around 8 weeks so I haven't pushed my Dr. for one. If you have an early ultrasound (in the fifth week) you most likely will only see the Fetal pole and might not hear the heart beat. This tends to worry some women so they ask for another ultrasound the following week.
I'm not sure if they meant the age of your baby from conception or your LMP. I suggest you type in your LMP into a due date calculator so that you can get an idea of how far along you are. Best of luck with everything! It's so exciting, scary and wonderful!
Oh and Congratulation!!!!!
I agree with darkestlight, I feel like so many people get worried for no reason when they have an ultrasound done so early, wait until 7 weeks.
If you don't want to freak yourself out I'd wait till week 6 or better yet 7.