I Will Be 64 Next Month. I Am HIV+. Otherwise,

I will be 64 next month. I am HIV+. Otherwise, I am in great health. I work two nights a week at Walmart doing maintenance - mainly removing trash from trash cans inside and outside the store, so some heavy lifting is involved. Two weeks in a row, after working the first night, I experience pain in the area of my right kidney and right testicle. This past week, the pain was so bad, I had trouble getting to sleep. When I go to work, the second night, the pain begins to ease and by the time I get off in the morning, the pain has all but disappeared. There is still a small amount of residual feeling - not really pain - in both the kidney area and testicle. I am sexually active one or two times a week and this does not interfere with my sexual life. Do I just need more exercise or is there a potential medical problem?