Bleeding and progesterone?

I am 8 weeks 5 days pregnant with twins after a frozen embryo transfer.  I had some bleeding at 5 weeks but the ultrasound at 8 weeks showed two strong heart beats.  Had more red spotting this morning and it just makes me nervous.  Anyone else experience this?  I am still using the progesterone suppositories and the nurse said those can cause spotting? I never had spotting with my first pregnancy and I hate it, makes me think the worse.