Why does my INR keep dropping?

I get tested once a week, and before they started the coumadin they did a full work up and nothing came back abnormal and they did a cancer screening and that all came back normal too. I was healthy until the PE and I wasn't on BC or anything like that to cause it. I'm seeing a hematologist for it and he can't figure it out either.

Oh no. When the hematologist is scratching his head, look out, lol. I didn't even ask about the pill because I figured you had already addressed that if it was a factor. I'm trying to think if there's anything I've ever heard about that could be the answer. I'll be back if I think of something.

I'm in the hospital right now on heparin therapy after a procedure. My normal coumadin intake is 6 mg for 6 days and 8 mg for one day. The hospital has been giving me up to 9.5 mg and my INR keeps dropping. After several times of asking why this is happening and getting "we don't know" as an answer, I started doing some research.
Some antacid meds like protonix will not allow your body to absorb coumadin properly. Once I told them this, they kind of panicked, raised my heparin therapy to prevent a stroke and I told them to stop the protonix, well, honestly, I refuse to take it. I believe that my INR will stabilize. Are you taking any medication for acid reflux, hiatial hernia or other gastric upset? It can be over the counter meds for gastric problems too. Check anything and everything you are taking to see if it is affecting the absorption of the coumadin. The answer may be found in new research too. Good luck.

Did either of you ever figure this out?
I also am generally healthy, not on the pill, and recently had an unexplained Portal Vein Thrombosis.
(Who knew that was even a thing?)

On heparin in the hospital I got within range in about 2 to 2.5 days. I started Lovenox injections and warfarin 5 mg / day at discharge. My INR is checked every few days, and was initially rising... 2.1 to 2.5. Then about 2 weeks after stopping the Lovenox injections, my INR inexplicably dropped to 1.6. No increase in exercise, no medications whatsoever (no antacids, NSAIDs, no supplements), and I am very careful on diet. They upped my dosage of warfarin alternating 7.5 mg and 10 mg, and it still went down further. So back on the Lovenox... which is neither fun or convenient.

I really just can't think of what I'm doing wrong, and I would really like to get this stable and high enough that I can have a salad and do some light exercise!