She could be teething, some babies are born with teeth (quite rare).
My 1st ds was teething or had symptons very early on and now my 2ds has all the symptons too and he is 8wks.
My 1st didn't get his 1st tooth though until he was 7 months but we didn't hardly have too much trouble with him. We used "ashton & Parsons"powedrs on him and will be giving them to ds2 soon i think.
You can use these from birth and they are herbal. You just give half a pack in the morning and half at night, but when they arer older you can give more (read the label).
They only cost about Ģ3 for a box of 20 and you can get them anywhere, tesco, asda, boots (if u are in uk).