Cheryl and I were just talking about how when you are reading through the Bible in a year and have a schedule where you read 5 Psalms a day you don't notice the recurring theme as much. (I didn't want to say they were repetitive. haha)
Jesus encouraged us to continue asking - to continue to pray.
Luke 18:1 Now He was telling them a parable to show that at all times they ought to pray and not to lose heart, 2 saying, "In a certain city there was a judge who did not fear God and did not respect man. 3 "There was a widow in that city, and she kept coming to him, saying, 'Give me legal protection from my opponent.' 4 "For a while he was unwilling ; but afterward he said to himself, 'Even though I do not fear God nor respect man, 5 yet because this widow bothers me, I will give her legal protection, otherwise by continually coming she will wear me out.' " 6 And the Lord said, "Hear what the unrighteous judge said ; 7 now, will not God bring about justice for His elect who cry to Him day and night, and will He delay long over them? 8 "I tell you that He will bring about justice for them quickly. However, when the Son of Man comes, will He find faith on the earth ?"
Jesus wasn't comparing God to an unrighteous judge. He was saying that if an unrighteous judge who does not fear God or respect man will answer a widow's petitions, how much MORE will God answer and bring justice to His elect.
So if you are going through a tough time right now (or when you are later - EVERYONE does and will) keep praying. It's OK to repeat yourself. But notice that David - even while praying the same prayer again - doesn't lose faith or hope.