If you are completely leaving it alone then that is normal . I also used to get that underneath the scab for 3 weeks and then on the fourth week the liquid stuff was not there underneath the scab. After few weeks it goes away . I also don't know the reason for it but it goes away. I would not suggest you to completely leave your lips alone. You can leave them alone with keeping them clean by washing your lips with very mild soap else ec spreads to healthy parts of the lips.