Although at this age babies just get more efficient at nursing and can nurse in as little as 5 minutes, if you get a sore breast, you could have to do something about it.
What you described looked like a beginning of mastitis but seems like you took really good care of yourself and prevented it. THe key, if this is mastitis, is to make sure you drain your breast, hot compress was also a good idea.
I had mastitis when my dd was 2 months old. It also started with a sore boob and soon the fever followed together with muscle aches. I was feeling horrible. What helped was frequent nursing, pumping the sore breast to make sure it is drained and taking rest/sleeping. I didn't get any antibiotics and I felt already better on a 3rd day.
To make sure he drains your breast you may need to do breast compression, for info on how to do that check this link:
http://www.kellymom.com/newman/15breast_compression.htmlHope this helps,