Yes, it sounds like it might be a blocked duct or mastitis. Do you have any lumpy bits in your breast? When I get mastitis and blocked ducts, I get a red spot on my boob, which is hot, lumpy and sore to touch. I also get hugely high fevers and flu like symptoms, like headache, aches joints, lethargy, runny nose. Maybe try to massage it. A heat pack or cold pack can help too. I like to have a shower with the shower head on the sore spot and massage it. You can take paracetomol and ibuprofen (nurofen) to help with the pain. If it is mastitis and gets hold of you you will feel like you've been run over by an mack truck! I think expressing to get the milk moving would probably be a good idea, to try to prevent mastitis getting hold of you, it can make you very sick, it sounds to me (though I'm not any kind of professional!) that your breast is full. Hugs hun.