You didn't give us much to go on, like size, condition, pot size, etc. Just from the date that your provided (2008) and the soil that you used, I would suspect that your tree would benefit from attention below the soil line. Slip the tree out of the pot and take a look at what is going on: circling roots, sparse soil, collapsed soil. If you do indeed need to repot, search in this forum for container soil types that have been successful for citrus. Whatever you decide, make sure it is well draining.
Barbara