I have this problem after my son was born.
I tried different methods, such as body massage, 針「久」, exercise, swimming, use of essential oils...etc.
I think the most important is to do exercise to stretch and strengthen your muscle, swimming is excellent. try to use good position at home, not to hurt your back, and avoid holding bb with bad position or long time.
use body oil with chamomile essential oils will help as it is good for inflammation and calm the sored muscle.
Now, I try to spend 10-15 mins doing stretching exercise at home everyday