Decreased Breastmilk

My baby will be 2 months old come April 10. I have been expressing/pumping breastmilk and is feeding my baby through a baby bottle. However this past few days my milk supply has been decreasing rapidly. I usually pump every 4 hrs and can produce up to 4 oz but now I'm already lucky to get 2 oz every 4 hrs. I started supplementing formula last week due to this and I'm afraid I might eventually fail to feed my baby with breastmilk. Guilt consumes me at the thought and its making me frustrated all the time. I don't think its good for my mental health. Ok lang ba mag formula nalang ako? I found this online (pic below) pero I'm not very convinced yet. Thanks sa mag respond.