Loss of appetite, chewing teat, 3rd month

My baby just turned 3mo few days ago and recently it’s been tedious to feed baby (bottle feed) since the estimated 3rd leap for him. He can usually drink 120ml each feed but recently drinks poorly- suck one time then stop, chew teat, look around, can take at least 45min and may not even finish full feed. He is taking slow flow hegen teat as he cannot upgrade yet (sputters, coughs and leak milk from sides). Yesterday he just received his 3rd month 5-in-1 vaccine as well. Not sure whether this series of poor feeds it’s due to his 3rd leap or early 4th leap, or the side effects of vaccination itself.. Any mama experienced this? 😢