Hi @Isabelle
Sounds like things are rough, I really feel for you and I completely get where you're coming from, you're not alone.
I actually went through an incredibly similar experience at that age as well. I too received a diagnosis of Fibromyalgia, but I'm not a 100% sold on the diagnosis to be honest. It was a conclusion they drew after a good year of ruling out other conditions.
I'm now 30 and no longer working in a place that causes me terrible pain. When I was at work and miserable, I was the same way, trying to do as much as I could but it cost me my physical and mental health. I very near committed suicide--at work--because I became so depressed with both my condition and the fact I just couldn't do things that I used to. Something that stuck with me is something a coworker said, "No one else is going to stand up for you, no one else is going to take care of you, you have to do that." I realised noone at work gave a shit about my condition, so I had to start. I was terrible at standing up for myself back then and I hated putting my foot down. When I finally quit my job the weight that came off my shoulders was incredible. Even though I'd had a serious lapse in judgement and had gotten so close to offing myself, I didn't realise how badly things were affecting me physically and mentally. So I'm going to echo what my coworker said; No one is going to have your back, only you can take care of you. And no job is worth sacrificing your mental or physical health for.
Now it's been a good 4 or so years since I worked at the place where this all started, and I still feel the affects. I still can't do things that I used to, I still find myself in pain. But I'm still not sold on the diagnosis.
You mentioned an abusive father, this is important. I've spent the past few years trying to take care of my mental health and deal with past trauma. I've come across some interesting research that there seems to be a correlation between adults who have lived through chronic abuse/trauma as children that then go on to suffer from chronic pain. A lot of abuse survivors tend to have inexplicable aches and pains, particularly around the neck/shoulder/back where we tend to carry our stress and tension. I also read that a lot of people who are diagnosed with Fibromyalgia had experienced an abusive or ongoing trauma in their childhood.
Now, I'm not a doctor or expert on any of this, at all. But as a person who is so tightly wound that I have to make a concious effort to unclench my muscles, it makes sense to me that they're going to be in pain after 20/30 years of tension. I couldn't honestly say one way or the other if the pains I get are a physical condition or if they're the result of my childhood.
Anyway, sorry, I think that went off on a tangent there.
And after making you read all that rabble, I really don't have a lot of advice to offer. All I can do is beg you to stop putting yourself through unnecessary pain, being in pain when you're trying to do ordinary tasks others take for granted is punishing enough. Show yourself some kindness and learn to accept you are going to need breaks, rest and time out. When I was working, I managed to change my roster to alternating days on/off so I could have a rest in between. Is this an option for you?
The hardest part of it all is accepting there are things you just can't do anymore because it's too painful. I don't know how to combat that, it's hard, it's depressing. But I have found new activities and hobbies, but I do miss the old ones.
I remember living with a hot water bottle and a bottle of deep heat close by, it helped manage the pain, but it doesn't take it away.
The comment you made about your abusive father stands out to me. Do you think this has had a physical affect on you at all? Do you feel tense? Do you grind your teeth? Maybe it sounds like nonsense, but in my case, I'd safely bet a lot of the physical pain I'm in now can be chalked up to past pain. Maybe I'm drawing that conclusion because it's easier to have someone to blame? Huh, hadn't thought of that before. Shit, that's not helpful.
Sorry, I'm going leave this now, sorry for all the rambling but I hope there was something helpful buried in my response. Even if all you take away from it is I've been there too, you're not alone.
All the best.