Baby Suddenly Loses Appetite

I have a 3 month old bottle fed baby. I am currently feeding his pumped breast milk and he's suddenly stopped wanting to eat. He only eats at night just before we retire to bed for the night and also once during one of his night time feedings. He barely eats 1 oz at a time during the days. I wonder what's going on with him. He hates his feeding position and rejects the bottle all together when i try to feed him. The only way i could get him to drink an oz or two is to put him on his swing. Have any of you experienced this?