TSH Level 26 is before starting Thyroxine 150 mcg or even after remarkable period of taking it. If it is after quite some time that you are on 150 mcg and still the TSH level is so high, then you need to increase the dose. May be you are taking it at wrong time of the day. It must be take on an empty stomach first thing in the morning. If you are not taking it that way, do it the right way,cwait for 4 to 6 weeks, recheck your TSH Level and consult again.