I have suffered from chronic constipation and rectal/abdominal pain for years since my 20s.
I had my first rectal prolapse repair in my 20s with biological mesh which I was warned may need replacing. It broke down and my symptoms of excruciating rectal and abdominal pain and incomplete evacuation began. I have just had a new tough plastic mesh fitted and am three days post op. The results are amazing already I can pass BMs without pain. I can recommend an Australian pelvic floor physiotherapist who posts free videos ''How to Empty Your Bowels Without Straining - on YouTube by Michelle Kenway". So for anyone suffering painful BMs this advice really helped me and I hope it helps you. The hospitals don't teach you how to go again after surgery and it is nerve wracking.
I was initially diagnosed with IBS years ago until someone asked me to 'bear down' and then they realised I had a full external prolapse. So if you feel a bulge in your bottom or like there is a tennis ball there when you sit up from lying down, do get it checked out.
I have to ensure that I never become constipated again as straining will damage me. So I am now experimenting with doses of movicol and will be moving onto stool softeners soon. Last year I thought I had a bowel obstruction as I didn't go for over a week and my 27 inch tummy swelled to 42 inches. I hadn't paid attention to my diet, fluid intake or BMs.