I have an inflatable lump over the left side of my bladder. Should I be worried (see a doctor)?

I'm 18 years old and generally healthy. I have had a small lump on the lower-left side of my bladder for about 4-5 years though. This small lump/bump/swelling is inflatable and deflatable, meaning i can consciously change its size. When i contract my stomach muscles it inflates and becomes bigger and when I relax it becomes smaller. By lightly pressing on it with my hands/fingers I can even make it disappear completely, at least until i contract my stomcha muscle the next time. So does anyone have a clue what this might be? Should I be worried? Also I should probably go see a doctor about it right?

Thanks in advance :)