Keep in mind, your menstrual cycle is determined by the number of days in your cycle, not by calendar months. So if you're counting by calendar months it's quite possible, given that February was a short month, that it's just a mis-calculation of when it should arrive.
However, if you're counting by days in your cycle, then it's probably just a slight fluctuation in the length of your cycle. It happens to everyone, and since you've been under a goddly bit of stress, that could also be affecting it.
Your pregnancy risk is really quite low, but if you want, you can always take a pregnancy test to set your mind at ease.
This link is useful for determining pregnancy risk: What's The Risk? - Five Easy Risk Assessment Flow Charts
"The only unnatural sexual act is that which you cannot perform."
-- Alfred Kinsey