Keeping track of derivations

Recently started research project as post-undergraduate working with quantum theory. A lot of time at the end of the day I end up with multiple half-filled white sheet of pages full of calculations, scribles, check-ups, which mostly do not get used. Next day I copy some "good" formulas onto the new page and continue, but this feels awfully messy and wasteful. I know, this might sound pretty dumb, but how do you go about doing calculations and organising work journals ?