Based on my last 3 periods could u tell me my ovulation dates roughly?

This is pretty regular to me. But you need to track more than just the start of a period to determine ovulation. Get a chart that has mucus type and basal temp. I had a book that had one in the back of it I enlarged. The book also had all the info on natural planning ie. everything related to a cycle. Sorry, don't remember the name of it though.