My cat seems to have a back problem?

it looks like my cat may have been in an accident. the back end above the hips is ached downward and not in line with the rest of the spine. she dosnt seem to be in pain, but is finding it difficult to spring up onto anything. There are no apparent abrasions visible and i need advice on possible problems that may occure in 4 year old cats. Also are there any over the counter pain killers available?