Why is my cycle going bananas?

You can certainly talk to your doctor about it, but it doesn't seem like anything is really wrong. From January to February you cycle was 31 days (normal), February to March is was 26 days (a little shorter but still nothing to worry about), the past cycle was 40 days long (a little long but until ti happens over 45 days multiple times something as simple as stress could make it longer), and you shouldn't be due for it again until June 1st. Yeah, it doesn't happen on the same day, but I am on birth control and I don't even get it on the same day every time. You should worry when you don't get your period for more than 45 days, and this happens multiple times. Things as simple as changes in exercise routines and stress can throw it off by a couple days. I wouldn't worry about it being pregnancy until you skip your next period which, 28 days, should be June 1st.