I had incredibly speedy relief from using cypress essential oil (pure)! I'm not even a super believer in natural therapies, but this one wasn't expensive and it worked. A tiny bottle of cypress oil (available at most places that have those racks of various essential oils - pharmacies, health food shops, etc) lasts for ages.

How to do the treatment. Just pour some warm to hot water into a shallow container of some sort (e.g. plastic marinating tray, even a baking tray), so it's a few centimetres deep. Drop in about 10 drops of cypress oil. Then sit in it for a few minutes, so the sore affected area has contact with the oily water.

Wash out the tray and do it a couple of times a day.

My problem disappeared by the following day, and didn't return till after the next birth. Same treatment fixed it again.

Good luck!