Sorry, don't have experience with TPO agonist drugs. I'm certainly used to platelets being hard to control, though. I know what you mean when you say "worked too good, then not good enough". My "drug" has acted like it was letting me down, but then I figured out it was me not taking it correctly.
Basically, I take the test only every couple of weeks when the platelets are high, but its not really often enough, if you look at my trends. You can drop from high to low in 2 weeks, even with some drugs, if its not enough of the right "drug". And there must be some hidden factors, such as infection that make your body require more. Maybe even seasonal allergies? If you require more than what you're taking, your platelets are going to drop. Its a very sensitive thing, apparently when using TPO agonist type drugs, too, if you're any indication.
My doctor sees my fluctuations, but doesn't suggest I take the blood test more often (when the platelets are high). It's almost like he wants them to go low. I don't feel its life or death, but its not the quickest way to really really figure things out. I do understand if its just trying to keep insurance happy. It takes months, or maybe its so sensitive and having other factors, that you never really get it figured out. Those unknowns will always be the wildcard, maybe.
One way or another, you're dealing with the unknown, and that is frustrating and a bit scary to think your options are dwindling. Like you say your hopes are dwindling when you see the surprises. I mean the disorder is not always difficult, but it is at times. Maybe it will get easy around the corner, or maybe it won't.
I've been at it for 10 months. I've figured out some things, as long as a curve ball isn't suddenly coming at me, but its still pretty full of surprises when trying to keep steady. That's the hardest part. Getting the platelets up is easy (for me), but I don't look forward to the times when I have to get them up. Fatigue and frustration are always in the mix at those times.
I would like to get the steady part right, partly because when the doctor wants me to get the platelets up, I feel pressure to get them up fast, since I'm not using his drugs. So I use far more "drugs" to get them up, than to keep the platelets steady, and I don't want to take more than I have to. Of course, I really don't want the platelets to hang around on the low end myself, either, so I have to take the bull by the horns, at that point. Its an interesting dynamic, for sure; platelets, real drugs, my "drugs", physician, blood tests...
All to hit that nice sweet spot in normal range, which, with TPO agonist drugs is not something you're necessarily shooting for the middle of, are you? Isn't NPlate supposed to be shooting for 50? I can tell you with my "drug", it would really be hard to stay around 50. I don't think I could do it. Mine is too reactive. 50 is not a natural number for my platelets on my "drug".