No; the fact that your OBGYN says you have a tiny uterus doesn't not mean you have an abnormally small rectum/anus (and this would play no role in constipation).
For many, two bowel movements a week is perfectly normal. Constipation occurs when having a bowel movement becomes difficult and has nothing to do with how frequently one has one. Neither has it anything to do with how painful an attempt at anal sex was. The assumption that one must have at least one bowel movement a day is inaccurate. How often one goes is dependent on how much fiber and fluid they consume, how physically active one is and can be affected by medications such as pain meds (even over the counter ones)
If you can pass stool easily, you are not constipated. If you find it hard to pass stool, purchase a box of Fiber One cereal, begin by taking 1/2 cup of this daily and slowly work up to a cup. You will notice more frequently trips to the bathroom within a few days of using this product.