Maybe try this,
In a prayer, ask God to use you. This is what I did and over time God gave me direction and purpose. "Lord, please use me as a tool as you see fit. I surrender to you Lord, please guide me and shape me in the way you want". Something like that. Let God be the potter, as you are the clay.
This way you will be aligned to do God's work so that you can confirm whether your selfish desires are just either getting in the way, or are truly in alignment to what God wants. The "follow your heart" idea is dangerous and not something I believe in anymore because feelings can be temporary. Make sure that your desires aren't just based off feeling, that one day you want to do that thing, and another day you don't feel like doing it. If God aligns you in a certain way you won't really lack motivation, your mind and heart posture will say "It would be a pleasure to do that thing for you Lord".