I had my period once last summer, hasn't come back?

hello, ok so last year when i had just turned 12, actually around the same time this year, i had my first period. it was really heavy but the next day it was gone. then i had again the next month (still during summer) but as soon as school started it never came back. i still had discharge and stuff but i never got a period. dont get me wrong, im happy about it, cuz i dont have to worry at school about pads and tampons but know its been over a year. i expected it to come back during summer since usually i play sports during school and i think that stress and stop it but it hasn't come back know that its summer so... should i be worried? oh im 13 right now btw.