Increasing TSH even after regular meds.

Hi Drs., I have a 18 months daughter, I developed Thyroid during pregnancy and it was diagnosed by my dr in the second month itself when TSH was found to be 43. I am on regular medications since then. Post delivery my thyroid slowly came under control and u still continued the medications as Eltroxin 50 which was advised by the doctor. For last 6 months my thyroid has been increasing even with relatively medicines for a marginal 5.5 TSH to now it has become 16.41TSH. My medicines dosage has also increased with time to now becoming 150mcg. Is this normal to have thyroid increasing so much even with regular medicines. Should I do some additional tests and is there some other way of treatment than increasing medicines dosage. Cause my thyroid doesn't seem to be going down even with increasing dosage.