Hello.., Gm..,
Usually during n after pregnancy many females have this complaint.., it is probably due to weak back n abdominal muscles..
Next Steps
Visit a experienced physiotherapist
Take modalities like IFT
Do supervised exercises with the therapist
learn N strictly follow posture n ergonomic advice specially of baby care
Health Tips
avoid forward bending frequently, bend from knees n not from spine
avoid heavy weight lifting
tc..