Sounds like the teething is the problem and his sore gums are putting him off feeding. It is possibly worse during the day. All you can do is try to offer him as much relief for the gum pain as you can and keep offering feeds. He should get back to normal once the teething pain is a bit better.
Get some bonjella or any other medication for teething and use it just before a feed to try and give him some relief then. Chill teething rings and let him chew on those just before you feed him. Look in your local stores and see if you can get a baby safe feeder
to put the frozen banana chunks in and let him chew on that before a feed top help numb his gums and give him some relief.