Hello and welcome to HCM forum .
From the clinical history that you have provided I can present the following most probable causes for your condition
1.Fordyce Glands ---Tiny yellow dots on the lips are called Fordyce glands ,these are these are basically visible sebaceous (oil ) glands . They are not usually visible in children, and tend to appear at about age 3, then increasing during
puberty and become more obvious in later adulthood.They are harmless and do not need treatment .
2.
Contact allergy --A
rash (sometimes itchy or painful )can also form if you have used a product like a chapstick, lipgloss or lipstick that you are allergic to, this is called a "contact allergy" . You should then immediately stop the use of that product and wait it out ,it may heal or may need topical applications like
hydrocortisone .
3.Infection ---A rash on the lips could be due to infections like viruses such as
herpes which tend to look more like small blisters that can often be painful or
warts, or from bacteria.
If the rash on your lips does not correspond to any of the above or is present in conjunction with any generalised rash on any other skin surface ,you should see a
dermatologist .
Hope this helped .