HI Suzanne, You are in exactly the situation where none of us likes to be with this disease - getting worse and getting inconsistent guidance from your docs.

As for being afraid of the antibiotics, Have you read the comments in this discussion?
https://connect.mayoclinic.org/discussion/macntm-is-different-for-everyone-treatment-might-be-different-too/
There is definitely a time and a place for antibiotics. I will liken taking them to a cancer patient having surgery only, radiation, chemotherapy or a combination of the three. Some slow-growing or early stage cancers can be treated with one method only. Others require a more aggressive approach to knock them out. There are side effects to treating, and then there is the very real side effect of not treating - spreading cancer, maybe even death.

So it is with MAC/NTM. Sometimes airway clearance with airway meds and/or saline can knock the infection down or out. Sometimes it doesn't work, and the antibiotics need to be considered. Yes, there are side effects, but failing to treat when needed has really bad side effects too - potential loss of all or part of infected lungs, need for a lung transplant, or if the infection invades too far, even (VERY rarely) death. So it is a balancing act.

This discussion contains links to some excellent resources that discuss the stages of MAC/NTM and the protocols on when to treat and when to watch and wait.
https://connect.mayoclinic.org/discussion/resources-for-the-abcs-on-bronchiectasis-and-mac-ntm/
You have told us your doctors are not specific on how much to neb, but what have they recommended using in the nebulizer? And have they prescribed a daily routine of airway clearance for getting the mucus out? It is the lovely, warm, moist breeding ground for bacteria in our lungs.
Sue