They never do unfortunately, they will measure you against the average absentee averages. Are they aware of the Fibro diagnosis? Have you provided them with any doctor notes when you called in to say you are not coming? They may give you a letter of expectation, if you have a Union make sure your shop steward is in your meeting.
Unfortunately there isn’t much protection when you have high absenteeism. Don’t argue just tell them what you experience and let them know you will try harder to attend. No need to expand further.
Don’t right fight as it won’t help your case. Just agree to try better and just continue to do what you need to do. All the best!

Thanks, just have to keep doing my best. I am not in a union, should i take someone else

They dont have. Disability at work policy. About time they did

My experience is that employers vary in their attitudes to fibromyalgia and general sick days taken. In my last employment organisation managers could refer their staff members for occupational health assessment to see if any changes in the workplace could be made, eg number of consecutive work days / split shifts, star & finish times, adequate & regular breaks etc. Does your workplace offer similar?
Does your employer have a policy regarding disability at work? If so its worth reading up to see if they are adhering to their policy.
If your meeting is classed as a formal meeting you should be abe to take a friend or relative with you. As you're not in a union maybe its worth contacting Citizens Advice Beauro (CAB)?
I'm sure you're already doing as much as you can & doing your best. Just stay aware of your own physical limitations & try not to push yourself beyond what is reasonable. Its too easy to push yourself too hard to try and appease others. Be kind to yourself as well as to others.
I hope all goes well for you.
Best wishes.