This happened to me 3 times during my 3 years of breast feeding. The first time was right after our son was born. He was happily breast feeding right after his birth and at home over the following 2 days, and then on the next day he tried to feed, became frustrated and start to cry. He didn't feed ALL day. I tried and tried, I didn't know what had changed, I was becoming so upset and he just cried and cried the whole day with me rocking him to sleep. Finally the lactation nurse returned my call and I went up to see her that evening. Although the day was just horrible and I was worried about him not eating at all, the answer was glaringly obvious to anyone but a new mom....my milk had come in.
Boy, did it come in! I had enough milk to feed every baby in a 12 mile radius. My breasts were so engorged that my little bub couldn't grasp the nipple to drink. It was stretched so tight. My lactation nurse, Dot, taught me to hand express before each feed to release some milk so that our son could latch on. She taught me right there in her office, and we put Lincoln on the breast right away, he fed, and fed, and fed and fed and then passed out exhausted from screaming and starvation. Poor tiny little man. I felt so relieved and so stupid that I couldn't figure that out myself.
Nevertheless. If your newborn has stopped feeding, make sure he is ABLE to attach first. If it's too hard for him, express before each feed. Dot taught me to express enough to fill one breast pad. I was doing this at first and then realised I should be keeping this white gold, so I began expressing & freezing which was really handy once I began to leave him with Dad over feeding times.
To hand express, put your thumb and forefinger on the outter sides of your areola and pinch down into the breast, almost like you're trying to get behind the nipple and then pinch outwards.
TIP - Once your baby begins to eat solids, adding breast milk to baby cereal, mashed veg etc is a great way to keep getting breast milk into your baby.
The second reason your baby might be resisting to feed is if you've eaten something spicy. My husband and I went out for an Indian curry, no chili nothing to hot just a plan curry but the next day, I couldn't get our son to feed. He would latch on and then pull away and cry and fuss. Eventually I worked it out. I expressed a full feed from both sided and threw it away. After that he feed as normal. Some babies, are fussy! If you've had chilli or spices or something a little different to usual...you may have to 'pump and dump' as they say.
The last reason your baby may not be to happy to feed is when your cycle returns as the hormones can alter the flavour of the milk. For me this was around 12 months and he fussed for a day or so and then continued feeding as normal.