OUCH! Your poor nipples!
A lot of babies go through nursing strikes during this age, particularly when teething. Sounds like his teeth might be part of the problem - have you tried some Tylenol about 30-40 min before feeds?
Since he likes to eat when he's sleepy, you might try rushing in when he's just waking from a nap and getting him then. How's your supply when you pump? Some women notice a drop in supply when they get their period... I agree that it might be a growth spurt too and he's biting from frustration or boredom when the flow slows down. Watch him closely when he nurses, and if you see him stop eating and just nibble, break the latch so he doesn't have a chance to bite. If he does clamp down, pull him towards you body quickly - it should make him open his mouth.
How long ago did you start solids and when do you give them? You want to make sure he's not filling up on the cereal instead of milk.
This is pretty common for babies -you're not alone!

It's likely a stage - just a really irritating one! If it's a growth spurt, things should settle down within a week. Keep me posted on how you're doing! HUGS!