I've been told i have hypothyroidism, how come i don't have many symptoms?

Often mild: Many people with hypothyroidism have no symptoms or very mild symptoms. The severity of symptoms isn't directly affected by the actual thyroid hormone levels either.It is partly affected by how quickly the levels changed. A gradual decline can often go unnoticed even with pretty low levels, but people who have a sudden drop ( like after surgery) are often more symptomatic.

It is variable: The way hypothyroid persons feels is quite variable. Some feel very tired with small degrees of hypothyroidism, but I have seen people who were deeply hypothyroid by blood tests, feeling nothing at all. When hypothyroidism is significant in a young person, (tsh>10) treatment is recommended even if the patient feels well, because it can cause high cholesterol and possibly heart disease.