What are problems in men that causes constant trips to bathroom?

Prostate, UTIs etc. Commonly prostate enlargement, mostly benign prostatic hypertrophy which comes with age, also prostatitis and prostate cancer. Cystitis or urethritis including stds. Bladder stone. Caffeine & high fluid intake. Anxiety. Occasionally: urethral stricture, bladder diverticulum, bladder reflux, interstitial cystitis.
Prostate; diabetes. As men age, the male hormone causes the prostate gland to enlarge; since it surrounds the urethra, it can narrow this tube & press into the bladder wall & prevent complete bladder emptying; thus the man feels the urge to pee more often & urgently. One of the signs of diabetes is urinary frequency. Urinary tract infections (uncommon in men) are possible cause too. See doc for eval for these issues.