Help? Back problems???

OK so my lower right side back has been hurting like aches like on and off for about 3 weeks. Like it will hurt for like half the day one day and then do the same thing just 3 days apart ish. But today it wasnt hurting and when i was horseback riding (which i usually do - just havent been in 2 weeks) i had to reach over while trotting and pick up a frisbee off the pole and when i did that the same place that my lower back was aching before, got this really sharp shooting pain. Well, i'm home now and it reaaally hurts badly. What could this be? All i did was reach over and not even that forceful or anything. I cant go to the doctor. So help? Also, i noticed recently that my shoulders are uneven. My right one is lower. But people are just saying that its cus im leaning and putting my weight on that side (which is the same side as my back.) BTW my mom thinks my back was aching cus of the way im sitting but i see nothing wrong. She doesnt know about the sharp pains today so i dont know if that will change what she thinks. THANKS!