My LO has been fed with Aptamil since 8 weeks old. She is now 20 weeks and has not been feeding well for a few days. Today she became completely hysterical, refusing to feed even though she was definitely hungry. DH suggested trying a carton of pre made Aptamil instead of the bottle we made up from the powder and she took it no problem. Half way through that feed we offered the original feed again and she started screaming again! What is going on???