Why is one breast having so many spasms?

I am 4 weeks post breast reduction and while my left breast is healing fine my right feels like there's a tennis ball in it and gets hard then soft .... continuously throughout the day. The left breast only has this happen 1- 3 TIMES daily. I've tried Massage and heat but nothing alleviates the discomfort I feel. When I told my Dr about it he says not to worry. Is this normal or should I request an ultrasound .

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