HI. The string like thing coming out of the urethra is a desquamated mucosa of the urinary bladder in response to infection called cystitis , a part of urinary tract infection or bladder cancer. Since you have excessive weight loss with difficulty in urination and stomach pain, the possibility of urinary bladder cancer has to be ruled out ASAP. I would advise you to consult an Urologist and get a physical examination, investigations of blood and urine, Cystourethroscopy and biopsy; CT scan of the abdomen. Further treatment will depend upon the findings; till then get started on an antibiotic and supportive medicines, take plenty of water orally.