How likely is it that using coles mouthwash gave me cavities?

Difficult to say: It is difficult to say if any mouthwash will give anyone cavities. Cavities occur when sugars from food are left on the teeth and allowed to create acids that dissolve the tooth structure. Acid conditions from soda, and juices that are frequently ingested can also cause decay. Check with your dentist to get even more information and help.

Probably not: I tried an internet search for coles mouthwash and came up empty. If it contains any sugar, then possibly, in combination with poor oral hygiene habits. Any sugar containing foods/drinks contribute to dental decay in the presence of bacterial plaque on teeth. Proper brushing and flossing will be your best bet against dental decay. Fluoride rinses help reduce decay also, i recommend them often.