What is a small purplish round pill?

It's most likely an OTC medication used for constipation:
"pms 411 small purple pill
small round purple pill, no scores, pms on one side and 411 on the other, this appears to be 8.6mgs of Senossides, a common over the counter laxative, a generic or store brand for Senokot tablets."
You could also ask a pharmacist if they recognize it.