Hi
Looks like oral mucocele,do not bite ur lip.
It might be because of any trauma(injury) to minor glands present on ur lip,it is usually painless,it can be removed if you feel uncomfortable or else it ll resolve by itself .
Hope ur question is answered.
Next Steps
Kindly visit a nearby dental surgeon for physical evaluation.
Health Tips
*Avoid biting ur lip if u have any( to prevent/avoid lip biting habit , use
sugar free chewing gums)
*warm salt water rinse.