I got a IUD and I got it checked but my string want there & now I have to get a ultrasound to see where its located what will the doctors do about it?

Locate it. They will try to locate the iud by ultrasound. If it is in the uterus, it is fine, but it will requie a small procedure to remove it when you do want it out. If it is outside the uterus but inside your abdomen, it perforated and will require surgery to remove ( a laparoscopy). Or it may just have fallen out. In that case you will need to have altenate birth control.
Locate it first. More likely your iud was expelled and lost. An us is a good way to see if your device is still within the uterus. If it is, they may tease the stings out, leave it alone, or replace it. (i recommend leaving it if you're not having problems). If negative us, i would order a quick x-ray to prove it's not gone into your abdominal cavity. (rare but possible).