5'11" 160 and bodyfat that is "def not low".... How does that toss away my lack of muscle idea? That pretty much confirms the lack of muscle issue.
I'm going to give you honest feedback though even though, with all due respect, you're being a bit of a whiney bitch right now:
What were you doing that caused your chest pain? If your pecs are hurting then you can put ice on it if you'd like. It would help reduce any swelling if you had some sort of trauma (like dropping the bar on your chest or bouncing it off of your chest while benching)
EDIT: after re reading your initial post I thought of another idea. Maybe you are leaning out a bit and one of the places that the fat is coming from is your lower chest or "man boobs"... a lot of men store their fat in that area and maybe thats whats happening to you? In that case it would be a good sign that you're losing BF and it just happens to leave from your lower chest first.