So I am 19, I started my period when I was about 13. My period was regular up until recently. I had a period in January and I didn't have another one until June. So for like 4 months I didn't have a period. And I haven't gotten one this month. Btw, I am not pregnant.

We can't even guess. A few suggestions are anemia, stress, extreme exercise, and thyroid disturbance. Premature menopause (before 40, with the norm about 50) has occurred as young as 11.