Quite likely is. My midwife said mastitis (in the early days) starts as a flushing of the skin before it really kicks in. You need to get that breast drained. Use heat before a feed to get things flowing, and cold after to reduce swelling. Rest, rest and more rest. Feed from that side first each time tip it settles (but keep an eye on the other side). Don't go crazy with expressing as well as feeding or you could set yourself up for more problems with oversupply.

Nurofen is great as it helps with pain and reduces swelling.

Hope you have a good night of sleep - well, as much as you can!