6weeks pregnant and bleeding I had an ultrasound today ...I'm confused

Martika
I'm 6 weeks pregnant (confirmed today)
I've been having pink discharge and spotting for 3 day now and it been worrying me so this morning I went along to my local early pregnancy assessment clinic and they preformed an ultra sound on me,
We see baby who is measuring 6 weeks and also seen the little heart beat, I was told all looks good atm and that they r happy with what they saw, but they didn't know where the blood could be coming from,
Don't get me wrong I'm so glad baby is in there and healthy, but I am so worried that I'm still bleeding and no idea y,
Have any of you ladies bled through ur pregnancies and went on to have healthy baby's 
Or what's ur experience? 
If it continues I'm going to go back in a few days