According to WHO mother can feed up to 5yrs age of child. Frequencies should change accoring to child age .good to have those medication during lactation period. So you can continue those medicine.
You should chek cause of low milk. Most of time they are associated mentally and physically problems. Or poor feeding technic.
You should consult to ayurvedic pediatrician doctor ,gynac or lactation consultant.
Next Steps
stay happy, increase involment in child, take good rest and quality food and most important "you are mother you are doing wonderful job ."