Dry mouth increases your risk for the bacterial infection "caries", that causes cavities.
Medications can increase the occurrence of dry mouth.
Sucking on sugar filled lollies to releave the dryness encourages the caries infection.

Looking for Dry Mouth relief?
Xerostomia or Dry Mouth, affects millions of people and is not only a source of discomfort but puts you at higher risk of developing cavities.  Dry Mouth can be caused by a number of issues:
Naturally occurring: predisposed to having inadequate or sticky (poor quality) saliva.
Medication induced: there are over 3,000 medications listing dry mouth as a side effect.
Cancer treatment: radiation and chemotherapy.
Genetic disorders: Sjogren's Syndrome, a relatively rare glandular disease.

Mouth Breathing
Regardless of the cause, a lack of saliva diminishes your body's natural ability to protect itself against cavities.  Saliva is a natural protective factor for your teeth, it helps clean and has buffering agents to help neutralize the acids from foods or those produced by acidic bacteria. It has immune properties and starts the digestive process.  The absence of saliva often leaves your mouth feeling uncomfortable and your teeth more vulnerable to tooth decay.

Cavities
Cavities are the demineralized areas, or the holes, that form in teeth and are the result of a bacterial infection known as caries. This infection takes place when the normal healthy bacteria are replaced by acid-producing bacteria. This shift in bacteria is primarily caused by two things:
Prolonged acidic (low pH) oral environment: contributing factors include a lack of saliva, and or a sugary acidic diet that encourages acid-producing bacteria.
Transmission: this infection is contagious! You can be infected by someone through exchange of saliva.

Drilling and filling has been the traditional method of treating cavities, but it doesn't treat the underlying cause, the bacterial infection. Brushing and flossing has been the traditional method of prevention, but it does not change the pH (acidity) of the oral environment or treat the infection once it exists.

Expert Advice
Visit a dentist who provides "caries risk assessment and bacterial screening", where they evaluate risk factors that can contribute to you getting cavities and offers treatment beyond "drilling and filling".

Limit your intake of sugar and carbohydrates within your diet, but also consider non-sugar containing acidic beverages such as diet and sports drinks, juices, coffee, tea, sparkling water, alcohol, etc.

Use xylitol gum or an alkaline saliva substitutes to stimulate your natural saliva production, this will also help to limit the production of acid bacteria.