How long is brown discharge considered normal?

I am currently 7w5d. Ive been experiencing brown discharge. No cramping. My doctor said as long as it stays brown, she is not too concerned. I have an ultrasound Wednesday.

My HCG was checked at 7w exactly (when I reported spotting) and was about 43,000. They did not re-check it and instead just scheduled my ultrasound.

Please share any experience or information you have.