Breast Feeding

I haven't managed to exclusively breast feed my son. Started with combining breast feeding and formula but as time passes I am opting to give almost formula only as my baby still remains hungry after breast feeding him and also since his milk intake is now increasing. My baby is 2 months and a half old. Whilst expressing milk with the pump I am noticing that my milk levels has dropped drastically. Only managing to express 60 ml with both breasts everytime I express milk. This is quite low when considering that my baby is now taking 150ml in formula milk around every 3 hours and sometimes even in shorter periods. Any suggestions of how I can increase my milk or there is no hope now that it has reduced to this level?