Baby on formula feed-36days old. Guide.

Hi everyone, My baby is 36days old, since last week I was able to breast feed my baby, expressing or direct, but since a week, I believe my milk is not at all sufficient to baby so I have to formula feed most of the time, I really want him to be on breastfeed and I am not able to, tried him feeding through katori Chamcha , but all the milk is draining out and he has been choking so have to shift to bottle feeding, Now since 3 days his stool color is green and yellow pellets in it, as said this week I am not able to give sufficient breast milk, and baby is mostly of formula bottle feeding, I maintain hygiene while bottle feeding, but every night I am feeling guilty that am I doing something wrong with my baby's health, he will be very hungry if i don't feed him properly, and only alternative is formula, how can I increase my breast milk please guide.