Tuesday - tired, Wednesday tired - time for a rest day?
You get fitter during your recovery days.
I've spent years trying to figure out how my legs and body react to training and am still a bit mystified how it works. I suspect a lot of it has to do with external causes such as stress, diet and sleep amongst other things. Most of the runners I train with at the athletic club run much more than me each week so I'm not sure if it' the training volume (although I am a lot older than them all!). When I'm running well I find that I can train all I like and don't get tired but then go through long periods of tiredness, mush of which relates to periods of stress etc. I do however have easier weeks, but don't always feel better for it. Still a mystery to me how it works!
You're "a lot older than them all" - age slows down recovery - so you can't do as many tough sessions and can't do the same volume at the intensity of previous years.
Training is merely one of many stresses - as you note, work stress, diets keep etc all add onto it.
An easier week probably lets your body relax and unwind a bit - so it doesn't feel any better immediately (but see note about longer recovery above...) you either need to have a longer recovery period (no hard sessions, low volume) or time your recovery so you get races at the best point for you - maybe a recovery 2days off and then 2-3 days normal training will give you peak shape, you'll need to experiment and see what works for you.