Good evening, we're on the fourth month now, in a couple of days it will…

Good evening, we're on the fourth month now, in a couple of days it will be our last month. The last few days when he sucks on the breast cries, gets nervous, then pulls away from the breast, sucking and crying, maybe there isn't enough milk? Or is he sucking everything up and nothing is left? Please tell me what this could be? Before that they were eating normally calmly.