Talking with the endo is important. Possibly, a conversation with a pharmacist could help as well. What needs to happen is for you to put on your "detective" cap and try to figure out if there is something you are doing that might be interfering with the absorption of the replacement hormone into your blood.
Is there any other medication being taken that might be interfering?
Is the replacement hormone being taken first thing in the morning, on an empty stomach, and waiting at least a half hour before eating ANYTHING?
Typically, when something like this is going on, an analysis will show that another medication, vitamins, calcium supplements — things like that — are being taken too soon. Other issues could involve antacids, perhaps.
And, are you on a brand name of replacement hormone, or are you taking generic? Pharmacies can buy generics from different manufacturers at different times. That might be at play if you are taking a generic.
It is this type of detective work that might be necessary to figure out what is going on.
If, however, there is nothing like these possibilities happening, then perhaps you are just going more and more hypo, and need to take a larger dose of meds. Some of us DO continue to go more hypo over time as a result of the antibody action. I am on a much larger dose of replacement now than when I first started.
