Please Help. My dog is 11 years old but has recently started licking everything she comes into contact with.?

She's licking floors, inside shoes, chairs, tables, absolutely everything she can reach. She's also started eating random things off the street. She's even started eating empty snail shells from the garden. She's being fed enough, infact we're feeding her more to stop her doing this and she also has plenty of water at all times. She doesn't seem to be suffering from dementia because she's still the same dog in every other way but we don't know what's wrong with her. She's also been shaking constanly for about 18 months now .Her whole body quivers. It's like she has parkinsons although she does't shake when she walks. She's a jack russell by the way. Thanks.