26 events an hour is near the high end of moderate, getting close to severe (which starts at 30). So that's likely the reason (or a major reason) you are feeling fatigued. The Respironics System 1 is a good machine and should be able to get normal obstructive apnea under control. The treatment does take some getting used to, and for some people this can be difficult. But your health is at stake, and if you have a family to look after you need to ensure your health is looked after as well.
The first and sometimes the hardest thing is to have a comfortable mask which fits nicely and doesn't leak. If the mask is uncomfortable or doesn't fit properly, then everything else is wasted. Make sure you're happy with your mask, and if not try to get it changed. You didn't mention if you have insurance or not, but try to get your mask from a DME who will provide a 30 day return guarantee. Try as many as you can to make sure you have one which is really suitable for you.
Second is your bed and pillow - it goes without saying these should be comfortable and the bed should be supportive. If you sleep on your side (which is recommended for apnea) make sure your pillow has enough flexibility that it doesn't push the mask off your face. Make your bedroom as dark and quiet as you can and practice good sleep hygiene. See some good ideas here: https://www.betterhealth.vic.gov.au/heal...ep-hygiene
Also, position your machine so that the hose is comfortable and doesn't drag the mask off your face or get tangled up.
Next, check your pressure. Your profile says its 5 - 6, which seems very low. Ask your doc for a copy of the prescription and confirm that the pressure is correct. If it's too low you won't be getting any benefit from the machine, and you may not be able to inhale easily through the nasal pillows.
Then check your humidifier. If it's too low you will get a dry throat and congested nasal passages. If it's too high yu might get rainout, drops of water coming through the hose and into your face. This will vary with ambient conditions and your own personal preferences.
I hope this helps. Please come back if there are other issues you'd like to cover.