Chest pain after bowel movement? have been slightly constipated lately. is this the cause or is it something else?

Probably unrelated: I believe it is coincidental that you noticed chest pain after a bowel movement. Straining to pass stool does increase intra-abdominal pressure, but it would be unusual for this to cause chest pain, especially in a young woman of your age. If this is the only time you have chest pain, I think you can watch and see what happens. Work to relieve your constipation with more water, fiber, exercise.