I never had any std . what caused me to have an ectopic possibly?

Ectopic pregnancy: While scarring in your fallopian tubes from sexually transmitted diseases is a common cause of ectopic pregnancy, about half of all cases occur by random chance alone. Only 1 out of millions of sperm makes it to an egg. Of all the eggs that get fertilizes round the world in a day, some go the wrong way and miss the tube or don't get all the way in. Nature isn't perfect. Random events are natural.