well unfortunately it's impossible to diagnose this without a physical exam. any skin lesion that persists for 3 weeks is worth having checked out by a medical professional. you can start with your primary care provider or a dermatologist. i wouldn't worry about this too much in the meantime but i'd definitely make an appointment to get it checked. sorry i can't give you a better answer!
i have a white bubble bump on my lip. it doesn't easily pop and it keeps coming back. i've now had it for 3 weeks.