I have a bubble like bump on the inside behind my lip. i'm scared, what could it be?

Mucosal ulcer: It could be an traumatic ulcer which would require no treatment; it could also be a benign tumor or a cyst or a mucus cyst.

Likely mucocele: This is likely a mucocle. Rupture of a duct of a small salivary gland causes accumulation of saliva under the mucus membrane. It can be removed. Just popping it may not help. See this site for more info. http://www.ncbi.nlm.nih.gov/pubmedhealth/pmh0002605/.

Lip sore : Hi, it depends on how long the sore has been present. A mucoceole is a fluid filled blister or bubble that can form from trauma, or some viruses. Don't try to pop it, but if it doesn't go away on its own after 7-10 days see your pcp.