Why are you bottle feed you baby..!! It is not advisable I'm our setting to bottle feed the children...she should be on exclusive breastfeeding at present and due to any cause if it is not available then top feeding should given with katori/spoon. Your stupidity of using bottle will harm much more than you think than the stupidity of not sterilizing the bottle.
Next Steps
stop bottle feed ASAP. give frequent feed with katori spoon if BF is not possible.
start complementary feed after 6 month of age like cooked rice, cooked daal, khichdi Raab, halwa, cooked vegetables, fruits etc...