Transits usually activate whatever aspects we may have that indicate some potential for illness. Lower back problems are associated with the lack of emotional support so look for your Saturn contacts with the personal planets, especially with Moon and Venus.
Ascendant relates to your health and the 6th house to your potential illnesses. Take a look at their their rulers, position and aspects they make to other planets to evaluate possible health problems. Your 6th house may be ruled by Leo, often responsible for backache. It rules the upper back (dorsal vertebrae), but also Libra, as it rules the lower back (lumbar vertebrae), and Sagittarius (sacral-coccygeal vertebrae). Virgo rules the lower nerves of the back, so see if it’s possibly intercepted in your 6th house.