What can i do to help my spn nurse again?

Patient: My son was nurse fine than all of a sudden something changed and he refuses to nurse, What can I do to help my 8 month son nurse again?

Symptoms: My son is 8 months old and all of a sudden he refuses to nurse. He will look at my Brest and turn away and cry. He’ll take a bottle during the day, but in the evening he clearly want to nurse but won’t or can’t and he won’t take a bottle. What can I do? Ive tried nursing him when he is sleepy but he just knows. So he just cries to sleep.