Phil,
I’m no trainer, but maybe you should skip the next race so you can fully prep for your A race. With the amount of volume you do, I wouldn’t think you’d lose much fitness.
I eventually went to the doctor and found out that I’m anemic. I started iron and vitamin d supplements last week and feel a lot better. My power’s still down about 10% but better than the 15% from a couple weeks ago. Good luck!