You doctor is correct.

Nowadays most gastric leiomyoma are in fact gastrointestinal stromal tumor. Small tumors in stomach are relatively common findings during endoscope or on image studies. They are benign and no treatment is needed. If they are found 3 years ago and without changes with 随访& 跟踪, there is no need to worry about it. No food supplement, herbal medicine or any alternative treatment will affect them either. Relax and enjoy your life.