You said to me," I had thought it over before you asked."这句话

You said to me," I had thought it over before you asked."这句话的间接引语应该怎么变.
had thought 已经是过去的过去 在变成间接引语的时候是不是就不需要发生变化了?
为什么 before you asked的时态不需要变化？