Are you trying keto, fasting rides/trainer sessions, or other methods to lose body fat? If so, that might explain the vaguely "flu-like" symptoms and odd body odor. Many folks report similar issues.
If that's the goal -- losing body fat while training -- consider longer, lower intensity rides or trainer sessions until your body adapts.
I had similar issues when I tried fasting rides a few years ago. Cutting way back on intensity helped. But on days when I planned harder workouts, intervals, etc., I fueled up appropriately, plenty of carbs, etc.
And if your most recent COVID vaccine was less than a month ago your body may still be working on the immune system response. I had the Moderna jabs in April and May and I'd guess it took about a month after the second jab before I felt normal again. The first jab had minor side effects but the second wiped me out for a couple of days. But I had other health issues going on so I didn't push too hard.