low free testosterone levels why?

hello everyone im a 23 year old male heres my problem. iv been experiencing some symptoms related to low testosterone. so i went to my doctor and got my testosterone levels checked well i got the results back and my total testosterone levels are 6.49ng/dl which is a good total level but my free testosterone levels came back very low. my free testosterone level is 7.0pg/ml from a scale of 8.0-27.0pg/ml so clearly im very low for my age seeing that im 23 years old i think that i should be at the highest point of that scale. anyone know what causes low free testosterone. do i need testosterone replacement therapy or is there any medication that could increase my free testosterone levels.

[lowT]

Your free T level of 7 is very low for a 23 yr old im 37 and mine is 8.8 which according to the laboratory that did my test is low for my age they specified 10-28, different labs specify different levels due to different testing procedures.
I take it your total T was 649 not 6.49, 649 sounds fine so you have probably got an excess of SHBG (sex hormone binding globulin) your doctor should have explained this to you, it could also be an excess of other hormones most of these problems are manageable.
If your Dr has not orderd any further investigations i would go back and ask him to follow it up.