Breastfeeding and spotting

I am 6-7 weeks pregnant and have a 17mo that still nurses 2x a day. The other night he got sick so I nursed him all through the night...then started spotting brown blood the next morning. I have since started to wean him completely which he is not handling well. I had a miscarriage this past fall and am scared it's happening again. My hcg and progesterone levels were good yesterday but they have an ultrasound scheduled for tomorrow. Anyone else think breastfeeding can cause spotting in first trimester?