Although I’ve been training on TR for less time, your experience sounds a lot like what I went through. I asked a bunch of questions (see this thread if you’d like detail), but in the end the answer was the same one I’d suggest to you as others have:
You appear to be training too hard, and you don’t have the base for it. Your body can handle the intensity but not the cumulative workload… so you improve, you overshoot your fatigue limitations without realizing it, then you fall back and it’s hard to recover. It sounds exactly like what I did.
The solution to my problem was to back off the intensity for a while and focus on building a base: long, slow distance at Zone 2 power (roughly 60% to 65% power). This creates totally different physiological adaptations in your muscles and in your body overall, adaptations that are different AND complementary to what you get at high intensity. You really need to do both sweet-spot and LSD work if your body is not yet well-trained and well-adapted.
Since I’m in Miami, and it’s sunny/hot/humid and I always have winds, and I’m aging (48) and overweight (225 lbs), I targeted 65% power but with a HR cap at 75% of my max HR so I wouldn’t overwork myself. And then I just did miles and miles of “easy” rides… which were also kind of fun since I wasn’t working as hard and could watch the scenery and think a little.
A couple of months later, my FTP has rebounded to a new high (still just 199W, but my best yet!), I feel rested, ready to get on the bike, and I’m back to two 1-hour strength-training sessions (Tue/Thu), two 1-hour sweet-spot workouts (Mon/Wed), and one long/slow weekend ride to continue building that base. And I feel fantastic.
Your training is a marathon, not a sprint. First, rest and recover and shake off the overtraining… however long that takes. Then, build your base. Then you can come back and add some intensity back in, gradually. Do this well, and in 3-4 months you’re going to feel like a rocket ship.
TR is a great program, based on good hard solid science. There are other great programs, with slightly different styles but all based on similar science. I promise you are not facing a “TR is not for me” problem, just a “beat my body into a pulp” problem.