Why haven’t I got my period yet? I’m starting to worry!.?

Avalynn Asked: Why haven’t I got my period yet? I’m starting to worry!.?

Disclaimer: There is no possible way I can be pregnant. I'm a virgin.
So around a year ago the summer (June) before my Sophomore year in high school I finally started my period at 15. I am obviously a late bloomer, but so was my mother so I expected it to be normal. I went around 2 months without a period until I received my second period. From then on I was fairly regular, getting my period every month. Recently though I haven't received my period at all! My last period was in March and its already July. I thought simply irregularity, but if I go this whole month without a period that will be 4 whole months without it. I'm very active, I participate in sports like cross country and track. I'm around 5'4 and 107. I have lost maybe 1 to 3lbs recently but only because its summer and I've lost muscle mass since I don't lift weights much over the summer like I do throughout the school year. I've always been small and have eaten healthy, that's just the lifestyle my parents raised me in. I've not tried to lose weight or get to a low weight, I just naturally have a very small frame so I don't believe weight should be a issue. I do exercise fairly consistently over the summer, around 5-6 days a week. I'm not really under any stress. So what could it be? Am I just still very irregular since my period started barely a year ago? My mom isn't too worried, but I just wish it would come already. Advice ladies? Personal experiences? Anything and everything would be appreciated!