Hi sweety. I do not know the answer to your question regarding if there is any connection between constipation and vaginismus, but I researched the information and found out the following (see below). I hope this helps.
Chronic constipation – Constipation over a long period of time may damage the pelvic floor weakening it and straining the organs. An imbalance can set itself up further feeding in to the pattern of constipation where the muscle dysfunction has become the main problem.
Pain – Pain associated with pelvic floor dysfunction can be in the pelvic floor itself or can be referred with the feeling that it is in the anus or rectum or coccyx, the vagina, labia and clitoris in women and penis, scrotum or perineum in men. There is often associated lower abdominal pain and associated tension in other pelvic, lower limb and spinal muscles.
Though there can be an association between irritable bowel syndrome and vaginismus, constipation is not usually one of the associated conditions. It is best to manage constipation with a high fiber diet which would include the use of Metamucil (easier if taken with diluted juice) and a stool softener such as over the counter Colace.