I'm an 18 year old female and I'm concerned because I haven't gotten my period yet. I was concerned that I may be pregnant but I read that pregnancy is extremely unlikely if there was no penetration when the sperm was ejaculated. Even so I took two different pregnancy tests and both came out negative. I feel no pain or discomfort nor any emotional changes. I don't understand what it could be because I'm not extremely stressed. I have lost some weight but only due to a new work schedule that has me on my feet anywhere from 3-8 hours. Other than that, I do not exercise. I'm 5"1' and approximately 110-115 pounds so in not underweight. My eating habits are normal and regular. What could be the cause of this?