I have a bubble blister behind my lip (it is inside my mouth) it goes away and then grows back, I am concerned of what it could be.?

Get It Checked. There's no way to know what it is without seeing it directly. However, "bubbles" that come and go are generally not too serious. But, like all sores, bumps, lesions, blisters, etc, it could be VERY serious. The next time you have one, see a dentist, oral surgeon, or ENT. Then you'll know for sure and won't have to worry. He/she can maybe also recommend treatment so it won't come back (as often).