What Causes Pressure Build Up In Pelvic Region?

Hello, I am a 44 year old woman who has 3 children. Nine years ago, I had a twin homebirth with 2 large twins (9#5oz and 7#14oz). The 9# baby was first, and was breech. I had three midwives present, but not medicine, and it was a very difficult delivery. After delivery I had tears which healed naturally, and the midwives said everything looked normal when they checked me. I have never felt quite right in my vaginal area, and upon straining during bowel movements, I have had some part of my tissue press down into my vaginal canal. This would only occur on certain occasions, but for some reason the last 4 days, I have been having increased pelvic pressure. I did have a normal pap smear and pelvic exam in October of 2014. I am having bowel movements, and passing gas, and having no problems urinating. But have pressure build up if my bladder or bowel is full and this causes difficulty having bowel movements (no problems urinating.)