My chihuahua is having muscle spasms and jerking in hind legs and just by touching her back.i haven't money to?

i called vet,have no money,my dogs muscles are spasms and jerking on her back. and hind legs i accidently stepped on her going upstairs carrying things.she screamed but didn't start spasms till two days later.she is worse today.6 yrs. old.called vet.said she needs pain meds or nerve pills to.has anyone experienced anything like this with your dogs??is there anything at home i can give her,like asprin..desperate..don't know what to do for her..