Should TSH level of 5.8 and above be treated?

A normal TSH level is around 5.0, so I don't think that you should be treated if your TSH level is 5.8. You should see a doctor again and get a blood test to check your TSH. If your TSH level is above 6.0 the doctor should send you to and endocrinologist and if the endo thinks you need to be on meds like Synthroid or Levothyroxine or some other thyroid medicine he (or maybe your regular doctor) will give you a prescription. I'm sorry if I'm wrong, but I hope I've helped.