What Causes Spotting During 7th Week Of Pregnancy?

I started spotting brown blood I m 6weeks 5days pregnant I had an ultrasound done they said the baby is fine and we even seen a heart beat my hcg levels are in the 76,000s of that s what they were Friday when I went to the ER...my brown spotting is getting lighter and lighter but it smells is that normal or do I have some kind of infection