I'm afraid I'm not that informed... as in, I don't know why, or dosage issues etc., but I understand that it's recommended that you avoid taking Ibuprofen during pregnancy. Hopefully someone will pop in with some more info., but in the meantime, I would suggest going to your GP and having a chat about what you can safely take. I know a friend ended up on panedine forte for a toothache when pregnant... perhaps your doc can prescribe you something stronger than panadol that is known to be safe.

All the best for a quick recovery from your flu, and a happy and healthy pregnancy.