Throbbing left breast/chest pain, anyone else?

It started out of no where maybe about ten minutes ago. It's a throbbing feeling in my left boob and the left side of my chest. It feels like it's coming from within or under my boob/nipple. I'm 26 weeks. Of course, with my anxiety, I immediately think heart attack and become very nervous. But then I thought maybe it's pregnancy related? I didn't have this with baby #1. Has anyone else had breast or chest pain on their left side and it ended up being normal? I have a drs appointment tomorrow and will mention it but figured I'd ask on here to calm my nerves over night.