My DS2 did the same thing at about 6 months. I was all worried about him getting dehydrated cause it was really hot at the time so gave him little drinks of cold water when it had been a long time since his last decent BF. It only lasted a bit over a week... like some of the other babies he started crawling, got some teeth and then went back to feeding. Neither of my boys have been big feeders while teething, I guess it must hurt their poor gums.
I found my big, sore, full boobs were the biggest casualty, so my advice would be to keep expressing so you are comfortable and maintain your supply. Keep offering feeds regularly. If he isn't interested just leave it and try again later. I found my DS2 just got cranky at me if I kept trying to get him to attach. Try to relax and hopefully he will start feeding properly again soon.