Shaikh Ibn al-Jawzi (may Allaah have mercy on him) concerning this matter said:
"I think part of the test is when a believer makes du'aa' and receives no response, and he keeps repeating the du’aa’ for a long time and still sees no sign of a response. He should realize that this is a TEST and needs patience.
What a person experiences of "waswaas from Shayataan" when the response is delayed is a "sickness" which needs medicine, I have experienced this myself. A calamity befell me and I made du'aa' and did not see any response, and Iblees started to lay his traps.
Sometimes he (the accursed) whispered: 'The generosity (of Allaah) is abundant and He is not miserly, so why is there a delay?'
I (Ibn al-Jawzi) said to him: 'Be gone, O cursed one, for I have no need of anyone to argue my case and I do not want you as a supporter!'
Then I told myself: Beware of going along with his whispers, for if there was no other reason for the delay except that Allaah is testing you to see whether you will fight the enemy, that is sufficient wisdom.
My soul (nafs) said: 'How could you explain the delay in the response of Allaah to your du'aa's for relief from this calamity?'
I said: 'It is proven with evidence that Allaah, may He be glorified and exalted, is the Sovereign, and the Sovereign may withhold or give, so there is no point in objecting to Him.' "
May Allah increase us in Sabr, accept our du'aa's & send His response soon! :)