Levothyroxine?

So I have subclinical hypothyroidism according to my doc...on one test my free T4 was low and tsh normal and another free T4 was normal and tsh high as well as feeling cold, fatigue, and hair thinning. I was put on the lowest dose to make sure I can tolerate it since I'm just borderline. Can anyone tell me what to expect or how long it takes to feel a difference or even what to watch out for as far as side effects?