The soreness sounds like it is in the serratus anterior muscles. They originate at the ribs where you indicated and insert on the scapulae (shoulder blades). They help to prevent scapular winging therefore keeping proper articulation of the shoulder blade with the trunk. So, I think you're getting stronger Do you perform any kind of pulling exercises? In terms of food and the weekend mine sounds like yours. I overate yesterday and also stayed up too late.