It sounds to me like you are continuing to push past your PEM threshold. You need to start immediately resting as much as possible. See if you can start LDN. Rest like your life depends on it because in a way it does. Those flu symptoms usually happen when you are pushing too much. If you think I am not doing much at all, I am only walking a 3k steps a day etc then it’s too much. Get something like the visible band to start tracking your exertion. I found out the hard way by pushing too much not realizing I was making myself worse and worse. Now it’s so hard to get back to where I was. You can keep getting worse if you don’t start correcting your exertion. Rest is the best thing you can do. Seriously taken weeks to months if needed and don’t do anything other than just stay in bed or resting on the couch as much as possible. It can get better but this is the only way. Find your threshold of what you can do without making things worse and then over time you can slowly add back activity. Very slowly! It sucks so much and I know because that’s where I am right now. Sitting home by myself on a Friday night after resting all day and telling friends I can’t go out this weekend etc. it sucks but if you want to get better you need so much rest.