3w pp

I’m trying to exclusively bf but I doubt I’m getting enough milk

Baby bfs then after 5 mins starts howling so I’m guessing my milk is over so we giv formula as per pediatrician advice

But few minutes later my boob hurts and feels heavy

So I’m guessing I don have a let down

Can anything or anyone help with this

Wen I pump I hardly get 10ml from one side the left side and around 30 ml from the right