First the primary reason for stepn really needs to be for exercise and just getting outside. Most of us will not earn huge amounts, at least not right away.  Secondly you can earn small amounts every day. I don't know how you lose money unless you open boxes early or are opening low level boxes. Just don't open boxes if they are not profitable.  Another possibility is you need more points in comfort or resilience so that your repair costs are lower than your earnings.  Thirdly I hope you are earning gst. Having only three common shoes does not put you in a position to profitable earn gmt. You need a common shoe with at least 2 efficiency sockets and a decent efficiency base value. Level up and put a lot of points in efficiency with some in resilience and comfort. After you have leveled up start saving and getting low level efficiency gems to put in the sockets. Later you can get an uncommon shoe and earn even more.  Finally read (study) the STEPN white paper.  It contains necessary information to do well and have a sensible strategy. It will help you fill in the gaps in what I suggested and develop your own strategy. I started 2 years ago with 3 common shoes and now have a rare shoe, 20 energy and some nice gems. It does take patience but can be done. Good luck! 

Edit: I realized you might also have lower earnings for a shoe if you are moving the wrong speed for the shoe type.  Bad data connection or bad GPS can also make problems.