thyroid dosages

I'm so confused about the dosages. I'm on .137 mcg now. I've bounced between .125, .137 & .150 for the last 10 years. I just had my thyroid checked again and now the doctor wants to increase? or decrease? my dosage to .150 mcg. He said my thyroid count was high. So he is changing the dosage to 150 mcg. If the thyroid count is high does that mean the thyroid is not fast enough? I thought the lower the number the lower the dosage, which in turn would slow down the thyroid and the higher the dosage the faster the thyroid. I'm so confused. I get the feeling it's the opposite of what I think. Is .125 mcg higher than .137 mcg which is higher than .150 mcg and so on? Can anyone explain this to me in laymen's terms? I'd really appreciate it. slb