I admire you for being a teenage entrepreneur. It shows your courage and ambition.
To answer your question regarding motivation, let me share you my experience. When we start (any) project, we get motivated by goals that are ambitious, but also seem to be very far from us at the beginning.
The key to maintain high level of energy in the meantime is to celebrate every single small achievement or milestone you conquer towards your obejctive, conscious that every step, even baby steps are putting you closer to your main goal.
So don´t wait to get your final success to be happy, embrace and enjoy the journey, celebrating every single step of the process and sharing it with your network and peers. People reacts positively to those that are working hard to progress, and you´ll get unexpected support from them.
Have fun and wish you the best!
“Success is stumbling from failure to failure with no loss of enthusiasm.” – Winston Churchill
Good luck and go get em!