Um my back is numb!!!????!!!!?

well here's the story last year about november i was helping my mum, dad and brother move a solid wood bookshelf that weighed about 100kg by hand. and i tripped and i still had hold of the bookshelf and i pulled my arm and around about my shoulder blade started hurting like *****. i got an x-ray and nothing was broken so my mum told me to rest (shes a nurse) i used ice and everything. now about 5 months later when touched its numb like when you sit on your foot and it gets numb but its like that the whole time. and when you poke it it hurts like***** and it feels like there are pins and needles. i just want to know what it could be its about 20cm across and its really numb is it nerve damage and if so what can i do about it???? thanks (p.s. im 13)