I have experienced similar pain as you describe. Had to take a break for about a month, then got back into it. I believe most of my problem was conditioning. After I got over the initial “soreness” I have been able to run pretty hard with no pain. I am 5’9″ 142lbs. and use a Ribtect medium large seat with Ribtect 3 vest. It was still a little loose so I added Zoombang padding to the sides and back. I did try to go to a medium Ribtect seat but it was too small. I could get in but was noticeably tight. Seems I am in between the 2 sizes.