Are there doubts I shouldn't be having? How do we know when to just let go of a certain prayer?

If you have nothing to make you stop praying or He hasn't fulfilled the prayer, then keep praying. What messes us up is time, which God operates outside of them.

Prayer is a dialogue, not a formula. We have a relationship with him. Prayer matures us into an awareness of the multi-faceted nature of a God who loves us deeply, can be trusted fully, and is drawing us deeper. Every time we pray, we're wrestling with our faith, and that grows our roots.