Thanks for your question.
Taking medications and relying on them generally isn't the best long-term solution for insomnia. These medications are best used for a short term and intermittently for them to have an effect, or else tolerance may develop. Please ask your doctor for another type of medication used for insomnia, since these seem to be not working for you now.
Basically there is no minimum number of hours that one must sleep and anywhere between 6-8 hours is fine. However a basic amount of sleep is required to function comfortably in our daily life. And if you are feeling tired and sleepy during the day this can be due to inadequate sleep.
A sleep hygiene is beneficial. Some beneficial advice which you can try and see if they work are listed below, however don't try all of them at once and overburden yourself:
You must use your bed only for sleeping and for nothing else, and if you are not asleep after 15 minutes in bed, you must simply get up and do something else. Sometimes, changing to another bed or to another room is helpful. When muscle tension is prominent, relaxation tapes, transcendental meditation, and practicing the relaxation response and biofeedback are occasionally helpful.
Wake up at the same time everyday.
Stop using central nervous system (CNS)-acting drugs such as caffeine.
Avoid daytime naps.
A graded program of vigorous exercise early in the day.
Exercise regularly for at least 20 minutes, but exercise must be done at least four to five hours prior to bedtime
Avoid daytime naps, especially if they are longer than 20 to 30 minutes or if they occur late in the day
Avoid evening stimulation and don't do mind stimulating work at night such as reading. Try to finish all the tasks of the day early.
Very hot, 20-minute, body-temperature-raising bath soaks near bedtime may be tried.
Eat at regular times daily, and avoid very large meals near bedtime.
Progressive muscle relaxation, meditation, and other evening relaxation routines can be practiced.
Comfortable sleeping conditions are also helpful.
You may also ask your doctor about Melatonin which has been reported to improve sleep onset, duration, and quality. Patients who are older than 65 years of age tend to suffer from sleep maintenance insomnia, and in these patients melatonin serum levels have been reported to be low. Elderly patients with sleep maintenance insomnia who received melatonin preparations had improved sleep onset time.