K.R.
Hi there! I'm a lactation educator at A Mother's Haven in Encino. Does your baby spit up a lot? That combined with irritability during nursings and reduced feedings are signs of acid reflux. Most babies with acid reflux are healthy and happy and it usually resolves itself between 12 and 18 months.
Try nursing your baby in the football hold so that he is more upright. Also, try nursing him for a shorter period of time on each breast, but nurse him more frequently. So instead of nursing for 10-15 minutes on each breast every 3 hours say, nurse him for 5-10 minutes on each breast every hour and a half. When you lay him down for bed or naps, make sure that his head is elevated. Put a couple of pillows under the head of his crib mattress or you can purchase a sleep positioner that elevates his head (just need to elevate him about 30%).
Give it a couple days and let me know if it helps. If not we'll get it figured out! Talk to you soon!