You may take some yogurt, or kefir for diarrhea. 3 antibiotics could kill the good bacteria,which may be the reason of diarrhea. Do you think your insomnia is caused by the anxiety?When we hear that we getMAC very often we worried,I was. I take a little bit anxiety medicine which doctor prescribed.fatigue maybe caused by MAC disease. I am still doing exercises but in shorter time and 2-3 times a day.try to take a short nap after lunch .These are my way to deal with my Mac lung disease problem. Give me. Yogurt or for diarrhea right as you’re a girl that’s very good send it

Welcome to Mayo Connect - you have found a great support community for your journey with MAC. I think we are all very upset when we learn we have this - especially when we find out we are facing long term medication.
MAC is a rare infection, happening mostly in people with COPD, Bronchiectasis or Cystic Fibrosis. It is slow growing, so likely it was busy growing in your lungs for a long time before it was diagnosed. This also means it is slow to be cured, and you will be one the antibiotics for quite a while.
Here is a link to a discussion of taking the 3 drugs - others will have good tips to help you cope. https://connect.mayoclinic.org/discussion/drug-therapy/
You need to figure out what part of your feeling bad is the infection - which you just need to endure as you heal.
Fatigue and lack of energy are very common symptoms of infection, and your body is telling you to slow down - but not too much. But it is also a side effect of the drugs, so taking them at bedtime can help you to feel better during the day.
Diarrhea, and some nausea, are generally from the medication. You will need to do some experimenting to see what dosing order - time of day, etc help you. As @liangni1 mentioned, probiotics, yogurt or kefir can help. If it is really bad, talk to the doc about using antidiarrheal medication. Also, sometimes taking the drugs with a little food can help minimize the effect.

As for the insomnia, others here have mentioned it, but it is not a side effect of any of the antibiotics. However just your illness can cause stress and anxiety and the drugs can make it worse. That can lead to insomnia. This is a topic to discuss with your primary doc - maybe a temporary antianxiety med may help.

All that said, I need to ask a few questions so we can understand your situation - is your COPD stable, and do you have any other lung issues? How was the infection diagnosed?
Are you taking the meds daily or 3 times a week?
When you started your antibiotics, did the pulmonologist advise you to get your hearing and vision checked regularly? These meds can sometimes affect both, so it pays to be alert for changes and report them right away.

Please take a deep breath and get ready for this marathon - there are lots of us to help along the way.
Sue