7 weeks pregnant and spotting

Roxii
The doctors keep telling me everything is fine but I still can't get use to this spotting :-( I've been bleeding for a week now and although it's light it still worries me... I didn't bleed at all in my first pregnancy so once I saw the blood last week I rushed to the doctor thinking it was a miscarriage... I had an ultrasound and turns out I'm measuring small so instead of being 8 weeks like my lmp suggests I'm only 7 weeks. I'm trying to relax because I saw the little heart beat and my levels are rising but every time I see blood I get stressed :-( anyone else having spotting?