This past Wednesday, I got both flu and COVID. I did the same arm. Historically, the COVID vaccines have never given me a side effect--not even a sore arm. I always worried about that. But anyway, I haven't had a COVID booster since later 2021. OTOH, the flu vaccine always knocks me for a loop so I carefully plan when I'm going to get it. Generally I get the vaccine and then about 8 hours later I started feeling achy, slight fever, etc. This time was different.
I had the vaccines at around 10AM. Ran home and got on a virtual meeting. By the end of the meeting at 11:30, I had a wave of fatigue hit me (believe me, before that I was feeling JUST fine). All day I could feel it worsening but I was able to function and I don't think I had fever. By the time I went to bed, I was in full-on body aches--arm was fully sore. I took two ibuprofen and that really helped and I slept okay.
Next day, in the house all day, and I felt COLD all day. Like not normal cold. It wasn't chills though. Took my temp, no fever. Just could not get warm. Body aches and dull headache were there. Later in the day I took some ibuprofen and felt a lot better. By evening, it was like a switch flipped and I thought I felt normal.
Yesterday which was 2 days after the injections I woke up feeling normal/fine. I was sore under my arm but I couldn't feel a swollen lymphnode. Around lunchtime though, I got hit with fatigue and some body aches but they were mild.
Today (Saturday), the underarm pain seems to be gone. I still have a little arm soreness. It's early--we'll see how the fatigue goes.
I think most of my issue comes from the flu vaccine; however, it was different this year so I think the COVID vaccine did make it a bit different. Last year I got flu and Shingrix together and I had issues but nothing major.
I thought I had read that it's good to get certain vaccines together because they complement the immune response and make it more robust, but I think it's quite a different matter if one has a disregulated immune system.