Mastitis!

So we’ve been out all day and I haven’t really breastfed that much, about a couple of hours ago I noticed my right breast started feeling full and painful (normal if I’ve gone a long time without feeding) but i noticed even when I was feeding my son it was painful, I expressed some after putting him to bed and it’s worse, very painful and hot to touch, I feel run down too. I’ve googled it and sounds a lot like mastitis, What’s the best thing to do to relieve the pain? 😢😢😫 thanks 🙏