I frist got my period when I was 12. Since then, I have had my period every month; however, my periord never came on time. When I was in High School, I started missing my periods, maybe 3 times in a year. However, I believe I missed them due to stress. I am 19 now and have missed two months twice. I missed Oct and Nov. Then got them every month since then except now; I've missed March and am waiting for April. I am defenitly not pregnate. My sister had worse irregular periods and developed cancer when she was 18 ten years ago. I have also developed acne, which never was a huge problem for me. What should I do?