Swollen under armpit?

Melissa • 25 years old, first time mommy to a little boy named Noah 👶🏻
Hey! My son is a week old today and my milk came in a few days ago. Ever since it came in my armpit got really swollen on one side and I also noticed a lot of blood coming out in my milk one day on the same side. Is it mastitis or just a clogged milk duct??? It's starting to get painful just to put my arm down:/