Radiation Exposure

I have been having abdominal pain since January along with weight loss and no one can figure out what is quite wrong.  In the past 6 months here are all the tests that I have had done.
Jan 2007   Chest X-ray
Mar 2007   Upper GI Series and CT scan with contrast of abdomen and pelvis

Cancer - renal pelvis or ureter
Nerve supply to the pelvis
Pelvic laparoscopy
Pelvis x-ray

May 2007  CT scan of head

Head injury
Head and face reconstruction
Head lice
Indications of head injury
Radial head injury

in ER
June 2007  Radiation

Cystitis - noninfectious
Radiation therapy

given for Thyroid Cancer (100mci) followed with I-131 body scan
July 2007  2nd Chest X-ray with 2nd CT scan of abdomen and pelvis

Cancer - renal pelvis or ureter
Nerve supply to the pelvis
Pelvic laparoscopy
Pelvis x-ray

July 2007  Upper Endoscopy EGD

They do not want to perform another colonoscopy because I had one done in Jan of 2006 and it was clear

Clear by design
Clear eyes
Clear eyes acr
Clear eyes clr
Clear-atadine
Clear-atadine children's

and I am only 29.

I am now starting to worry because of all the tests I have been going through and the exposure to radiation.  How much radiaiton is too much?  I am scared that with all the tests that they have been performing my chances of getting cancer from exposure are greater?  Please offer your expertise in this area.