Try this on: next time you pray, realize that your answer has been sent. Immediately.
"Then said he unto me, Fear not, Daniel: for from the first day that thou didst set thine heart to understand, and to chasten thyself before thy God, thy words were heard, and I am come for thy words." (Daniel 10:12)
God answers prayer immediately. Obviously, there are manifold ways of looking at the topic. And I hate to proof text here, but we see from this verse in Daniel that the answer was sent the moment that Daniel "set [his] heart to understand". This is the same idea expressed in Isaiah (65:24) when God says "that before they call, I will answer; and while they are yet speaking, I will hear."
Granted, your answer may not appear the day after you pray. But if you have prayed according to God's will, know that He will answer you. This is where the struggle between our faith, our expectations, and time, comes in. And waiting is one of the strongest indicators of faith before God.
To continue with the shipping analogy—and this is kind of a stretch—but how much did you pay for shipping? If we pray half-heartedly and forget about the request, I'd have to say that it's proof that we don't really want it. Have you ever had God ask you a direct question? "What do you want?" And sometimes I'm speechless. "I want a black Porsche, please." But then I think Nah, He'd never give me that. Or, Maybe I don't really want that, what I'd really like is an extra-thick chocolate milkshake. I go all over the place with my undisciplined desires and I forget this most basic tenet of life: Contentment.
But there are things that we want, that we need. So Paul, speaking for God tells us this:
"Be careful (worried) for nothing; but in every thing by prayer and supplication with thanksgiving let your requests be made known unto God. And the peace of God, which passeth all understanding, shall keep your hearts and minds in Christ Jesus." (Philippians 4:6-7)
I suppose forgetting about what you prayed for might not be such a bad idea. That way, you'll be more surprised upon receiving your answer. But don't forget to thank God for whatever it is you want. It'll be there before you know it.
"the Lord rideth upon a swift cloud." (Isaiah 19:1)