Also, given the comment about Regumate, consider adding in Evitex. It’s a chasteberry supplement that works on the pituitary gland and helps to regulate hormones. They can be on both at the same time. My mare has really painful cycles and the Evitex made a huge difference for her. She’s been on Regumate without the Evitex and with it - both approved by my vet.
Personally, I believe that for chasteberry, you really need a high quality liquid form for it to make a difference though.