Just my own thoughts, nothing of what I am about to say I have red in a book so take it with a handful of salt. As I understand matter is a form of energy, not something that can be converted to energy. String theory suggests that all particles are made up of small oscillating "strings," I interpret this as all particles are not tiny little pieces of matter but tiny little bundles of energy, a way of relating electrons (an elemental particle) to photons (another elementary particle that einstein described as being a bundle of a wavelength along with being a particle at the same time.)
You could make the argument that all matter was created from all the energy that started say a first big bang since from my understanding matter and energy are essentially the same fundamental thing. Then you could ask the question where did all the energy come from but that would just start to be redundant.
Also completely off topic but aren't you just going into high school? How do you know physics 30 material?
