Ultrasound reveals mild bladder wall thickening. is it serious? as i m having frequent urination and swollen testicular veins after peeing.

Sounds like: Cystitis which is usually caused by bacteria and treated with antibiotics.

Bladder thickening: Thickening of the bladder by u/s is not an unusual finding, depends on how full your bladder is when doing the test. Your frequency of urination may be due to a uti, std, obstruction of some type. Those symptoms in a young man should be evaluated by a urologist.