Back Pain Following Free TRAM Flap

I had my free TRAM Flap reconstructive surgery about 18 months ago. Great result (lovely flat tummy!)and uneventful recovery. However, following pulling a muscle while gardening (in March this year), have had muscle spasms in my back, on and off and severe at times, which for some reason is exacerbated by swimming - breast stroke of all things! Has anyone else had anything similar?