@deestrada Here are a few questions raised by your post -
Are you seeing a pulmonologist who has experience with "refractive" MAC infections? Those are infections that seem to be gone, and then come back.
When you say that you have had 3 negative sputum tests, what was the period of time? The "gold standard" is to continue treatment for 12 months after the last positive culture.
Finally, has the cavity diminished in size at all during treatment?

Are you being treated by a pulmonologist who specializes in Bronchiectasis and MAC?