Don't know whats wrong

Hi! I'm an 18 yr old female and for the past week or so I've just been feeling weird. I have a really bad weak back, so my lower back always is hurting...but now my legs are really weak sometimes and I have this tingling/numb feeling. My arms also kind of feel tingly/numb but I don't know if thats just from carpel tunnel. It's weird and I don't know what is going on. Is it just my back that's making me tingle and feel numb, or is it something with my head? I stumble sometimes, but maybe its just because I'm clumsy. I don't really have headaches to complain about because they're never that bad anyways. Also when I'm sitting down, I shake my leg, but I've just heard thats you being nervous...I don't know what I'm really asking here...it's just plain weird!