These are pains that can be quite intense, that can move up and down the back, but that shouldn't worry you anyway.
In recent months, moreover, the growing belly forces the spine to a continuous effort and to a different position from normal: it is in fact natural to seek a more comfortable balance by moving the torso backwards and the pelvis forward. This position causes the continuous contraction of some muscle bands of the abdomen and back, which easily translates into a feeling of soreness or real pain in the kidneys.
The pressure of the pregnant uterus can cause sciatica, that is, pain similar to very strong "stabbing" that starts from the lower back, extends along one leg and sometimes reaches the foot.
To make these pains go away, a little rest in a lying position is usually enough, perhaps with the help of some gentle massage.
To prevent these pains, try to always keep your back in the correct position: give preference to rigid backrests, put a pillow behind your kidneys when sitting in an armchair or in the car so that your back is well supported; avoid the sofas where you 'sink'.
Wearing a sling or girdle regularly is useful as it keeps your back warmer and more supported.