I have a tiny clear bubble on my inner lip that slowly grew. Feels sort of rough when rubbed along my top lip. What could it be? No pain or burning.

Mgt. It may be a cold sore. I would advise avoiding acidic foods and using an over the counter medication. If it worsens or looks infected, please see your physician.
Mucocele. It sounds like a mucocele which is essentially a minor salivary gland which has become obstructed and slowly fills with saliva.
Mucocele. Probably a mucocele, a partially blocked minor salivary gland. But we can't see it or examine it. Let your Dentist take a look to do a proper diagnosis.