Well, one thing for sure, you'll never know which prayer God would grant and which prayer he would not. But actually, ALL of this prayer stuff, and I mean ALL of it, purely depends on your trust with God. To make it simple-sounding, when you doubt, what you actually believe is He may or may not grant your prayer, and even though you'd deny it, you don't really believe God can do everything. In your doubt, God will decide to hold on to your prayers until you start placing full trust in Him, and obviously that's not all! If you don't make an effort to increase the chances of getting your prayers fulfilled, why would God want to help? He would, again, hold on to your prayers until you start putting in the maximum effort you believe you can put in to your goals, and that's really it.
I don't know about everyone else, but I know that God helps me in every bit and piece of my life, even how minor as it appears, even if may not seem to be very nerve-wrecking, the things you personally face and get worried about are