How would I know whether I have incontinence or urinary retention?

Incontinence=wetting. Urinary retention = inability to urinate, or inability to fully empty bladder. A urolologist could help you with either or both problems.
Leakage. Incontinence refers to leakage of urine - either stress related ie cough/sneeze or urge - the urge to urinate and leaking before making it to restroom. Urinary retention refers to a neurolofical codition causing the inability to empty the bladder- which can cause leakage or not- usually does though...

Related Questions

Any tips for urine retention? I want it to control incontinence

Incontinence. See fp or urologist to determine cause of urinary retention. In females (especially after childbirth or hysterectomy) bladder "drops" (cystocele) preventing complete emptying & leading to overflow incontinence. Urologist can discuss options for treating the condition. Read more...