I agree to relax yourself in a warm bath or with a heat pad and some relaxing scent like peppermint or lavendar. If you honestly feel like it is truly a low dull or not so dull back pain that is constant then go in and get checked. I never had a baby yet, but you mentioned a daughter and so if you feels like it is the same and not stretching then maybe it is something to be concerned about. Not to alarm you, but my uncle's girlfreind just gave birth at 5.5 months pregnant on November 7th, so it is possible something could be wrong and better to be safe. I wish you the best and I hope you have some relief in your low back pains and that is all it is.
Take Care Meg.