Help! Where's my period?!

So a few basics, I'm 18 and not sexually active. I've had a history of irregular, heavy, painful periods. 
Starting this year, I have not had a single period except for spotting back in January. 
I've always been a stressed, moderately active person, so I thought I possibly was stressing enough for my body not to continue a cycle, but now that I'm out for the summer with little stresses, I'm extremely worried. I've never been to a Gyno, and am not too sure what could be the issue. Any advice?

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