Help me with advice. ? I always had enough milk, but yesterday I notic…

Help me with advice. ? I always had enough milk, but yesterday I noticed that I don't feel the flow (earlier this was exactly in this breast, sometimes there were painful pricks), plus some kind of bump between the chest and underarm. Yesterday it hurt badly, all night I did massage, gave the child, it doesn't go away. Literally the bump seems like milk got stuck in the ducts. All this has led to less milk in this breast. What should I do? What is it? To which doctor should I go ? Now I give the breast where the bump is tired sucking and falls asleep for 10-15 minutes, then I give the second one and it eats and falls asleep.