Hydroxyzine certainly is used for sleep. As an H1 antagonist (or inverse agonist) and 5ht2A antagonist (like trazodone) in can induce drowsiness through both mechanisms, especially in patients with comorbid mental disorders. You should start feeling something within 60 mins but if 150mg isnt doing it, more isnt going to help. You need to get that anxiety under control and find a more suitable sleep med it seems.
The bold sentences in your quote is exactly what I am trying to get accross to the OP.
The medication itself is well documented through science and we could discuss its sedative effects for the next 2 years, but from the way I read the OP I understood it in this way, " you have been given these tablets to help you overcome whatever it is that is causing the anxiety, stress whatever in your life. A doctor has hopefully prescribed these tablets for you and has given you a dosage schedule to follow and hopefully a follow up appointment to see how they are working".
I am not that doctor, I don't know what is causing your anxiety either.
I do know about Hydroxyzine, however, and it's sedative effects, but it is not a hypnotic.
The OP is looking for something to help him/her sleep and the way he/she is dosing themselves clearly isn't working, for that specific purpose.
Does the OP have anxiety or insomnia or both?
Did the Doctor prescribe this in order to help the patient through stressful situations so that a more natural sleeping pattern could slowly become possible after trying to deal with said situations, or purely as a sleeping tablet?
I certainly hope it isn't the latter (at this early stage of "treatment"), and only the OP can inform us on these details.
Until we get a response from the OP we are just speculating which is useless.
I agree that it can be used for sleep, don't get me wrong, I just hope the OP gives us a little more info so we can give the most accurate advise.
Hope you understand.