At this age they can go through a stage of feeding less during the day and more at night (due to distraction during the day). Being sick will also mess with things - snotty noses and sore throats make feeding uncomfortable. The sudden engorgement could well be due to a change in feeding habits (maybe less milk taken during the day?)
If your supply's been messed around (not sure that it has, but anyway) the best thing, as always, is to just feed as much as you can. Swapping sides if she's comfort sucking is good too, as kmn suggests. You'll need to give it a few days to see if it helps any.