Ouch!

So for those of you who don't think yoga is a real workout ... I hadn't worked out in almost 3 weeks because of the cold I had. I went back to yoga yesterday. And I took it easy. I didn't overly push myself. Today I am sore! My chest is a little sore and the part where my arm meets my arm pit is sore. I tried to figure out what muscle that is but the charts online don't specifically point to it and label. Is there such thing as pectoralis minor? I took anatomy in college when I thought I wanted to be a nurse but I don't remember much. (And yes, I hate blood and needles so what the hell was I thinking?)