There is an antenna amplifier behind the driver's side C-pillar. If you have changed your head unit and/or amplifier lately, you may no longer be sending power to the antenna amplifier. If this is the case, you will need to run a wire from your remote amp turn-on lead to the antenna amplifier, and all will be well. (I suffered with bad reception for about a year before figuring this out.)
If you have not made any changes to your in-dash or amplifier, then check for 12V at the power lead of the antenna amp. If there is power, replace the antenna amp. If there is no power, run a jumper line to the amp and see if it works.