What Causes Irregular Menstrual Periods?

my period was coming regularly up until March. It came around march 9- and left mid march. After that i didnt get it until recently, ( June 11th until june 30th). That alone wasnt normal and i was very worried. i had sexual inter course that weekend after it left and to my surprise i got it today again ( July 9th). Idont know whats going on with my body but if anyone can help please do!....i dont have insurance so i cant go to a gyno .I DONT KNOW WHAT TO DO!