Any idea what's going on?

A few days ago, I noticed my left shoulder started hurting a little bit every time I got home from horseback riding. At first, I figured it was just soreness from holding my shoulders back, even though it had never happened before. A few times, I would get a sharp pain in my left lower back or the same spot but in the front when I took a big breath. Not very often, though, and only when I completely exhaled. It kept getting more and more frequent, and now, it's at its worst; I can't really breathe without my left shoulder, the base of my neck, and those two spots hurting unless I am laying down. For those of you that are going to answer with "WE CAN'T HELP YOU GO TO A DOCTOR >C", I am planning on doing that tomorrow.