switch the types of soap that you use down below and see if that works.
If you douche, stop now. Also, avoid soaking in hot baths for any length of time, and do not use powder. After you bath, apply some A&D ointment and protecty our clothing with a mini-pad. Since I don't know your age or other factors, it is difficult to determine the cause. but this is a good way to treat it.
During the cold months, when the skin is dry, use a very mild soap. I recommend Dove or caress.
Try some aloe vera lotion or coco butter lotion that will help out. Try some cortisone cream first. It will get rid of the problem.