Six months is actually a really common time for teething to start, so it could very well be that! My girl was super fussy and drooly around that age too, and that was the first sign for us. You can try rubbing her gums gently with a clean finger or give her a chilled (not frozen) teether to help with the discomfort. If she also has a low fever or is pulling at her ears, it might be worth a quick trip to the polyclinic just to rule out anything else lah. Hang in there, this phase does pass!