Sounds as if teething is definitely having an impact. When Henry was teething he definitely seemed a little tetchy. Once that stopped (at about 5.5 months) he was fine.
I'd also recommend trying "leave it" training - play a bit of tug with a toy the dog likes and then stop and when the dog eventually stops give them and treat and say "leave it". This might help with the aggression thing, if they think they're getting something else.
Our last cocker had serious possession aggression issues, despite being the loveliest dog otherwise. He never had any toys of his own, so when he found a sock or tea towel he wanted to keep it! It wasn't very nice behaviour, so I'll be trying harder to do the leave it training with the current pup.
