Given the symptoms you provided (penis starts to expand into a ball like shape when start urinating), it seems possible that you might be experiencing meatal stenosis. Urethral meatal stenosis or urethral stricture is a narrowing (stenosis) of the opening of the urethra at the external meatus thus constricting the opening through which urine leaves the body from the urinary bladder.


It is very important when did you notice this condition first, because it is usually present in younger boys. The symptoms include: visible narrow opening of the meatus, discomfort when urinating, abnormal urine flow, possible bleeding during urination and more frequent urinary infections due to increased susceptibility.


You are advised to visit a urologist for a physical examination, urinalysis, urine culture, and eventually a renal and bladder ultrasound. If detected, urethral meatal stenosis might be treated with dilatation of the meatus in local anesthesia or with meatotomy which would require a minor surgical procedure to cut the meatus a little bit in order to widen it.