It is probably arising from inner ear pathology. Very often it occurs due to age related degeneration known as presbycusis. Also the neural cause is not unusual. A pure tone audiometry and BERA test will be highly helpful to reach a diagnosis. The medication given to you are at its optimal. It takes a few weeks to respond properly. In the mean time you can use some tick tick table clock or musical device or some noisy device in room while sleeping. It will mask the tinnitus (ringing sound). It is seen very effective in managing the sleep deprivation associated with it.