Blood in urine one day (also in semen) few days later blood clots in urine. Er doc said may have ruptured blood vessel. No pain whatsoever, worried.

Possibly... Could be a ruptured blood vessel, more likely in the prostate gland. Depending on your age and use of tobacco, if this recurs, it should be evaluated by a urologist (if over 35 y/o) or a nephrologist. Probably not serious if one time occurrence and no pain with urination or ejaculation.