For the last two days, my 12 week old ebf DS has been thrashing around like mad, kicking his legs about and punching at me, every time I feed him. He also throws his head from side to side, although he usually manages to stay attached while doing it (ouch!). Any ideas as to what it could be? He has also developed his first nappy rash over these couple of days, I don't know if that could be related?