What Causes Blood In Urine Post Workout?

Dear Doctor, Last year I had a persistant UTI diagnosis in Aug. [4 antibiotics} Swam in dirty wave pool. Blood @ work in my urine. Mopped amusement park restroom floors. Once again, a year later, blood in my urine? My symptoms only return after straining from lifting. New job now, stowing heavy products. Did have a complete hysterectomy 13 years ago. I am now 57, and have always been physically fit. [asthma only] Recent Dr. visits I had, hormonal dryness, twice a week using vagisil and urology appt. in November. Bleeding occurred 3 times this Friday night after stowing 75pieces @ 20# a piece, and another 75 piece count @ 12# a piece. Blood goes away after no heavy lifting. Has happened twice since I started my new job in August. Concerned and thank you, Respectfully, Deborah Reiprich