Milk won't let down

I breastfed my daughter who is 2 now for a year. I just had a baby August 5th and my milk came in yesterday but I feel like its not letting down. Its constantly full and after the baby eats I try to pump it out but I end up only getting like a oz all together out. I tried taking a hot shower before and doing warm compressions before feeding and drinking warm fluids but nothing is working 😬 my boobs are hard and I'm uncomfortable help meeeee! I've also been trying to massage them and nothing is helping