Lower back pain

Started back at the gym about 5 weeks ago.  A week and a half ago I pulled a muscle in my lower back but kept working out.  Later that day I tried to do a yoga class but could only last 15 minutes because of the pain.  Of course, all of this didn't stop me from doing a swim workout the next day despite pain doing flip turns.  Anyway, finally saw the light and laid off.  Haven't gone back to the gym nor done yoga. I only did one easy but long swim in the ocean.  Back started feeling better so I swam at the pool on Friday doing half the yardage, no flip turns and very easy, Saturday I went for a long walk, Sunday I mowed the lawn and other gardening and now my back is killing me.  I'm in my second day of doing nothing and first day using a hot water bottle. Open water races start in 2 weeks so anxious to get better.  Any tips?