My Last Blood Test Shows That I Have Sub Clinical

My last blood test shows that I have sub clinical hypothyroidism. I am a 58 year old female. The Dr. Has suggested I take synthroid for 3 months and recheck my blood levels. I have been reading about subclinical hypothyroidism and anything I read says it may not help to take medication. I'm not sure whether to start taking the medication or not. I'm also wondering if I start taking it will I have to remain on it long term?