Sharp pain

So this is my third pregnancy. I have a 19 month old, miscarried in January, and am currently 7 weeks with twins. Today I started getting a sharp pain that kept happening most of the day, below my belly button, just on one side. I had an ultrasound at 5 weeks, 3 days, and everything looked good. No bleeding, spotting, chills, anything like that. Could it be a miscarriage, or would an ectopic have shown up on ultrasound already? Trying not to freak out, but after a miscarriage I'm paranoid.