i wouldn't worry about pregnancy if there was no penetration. when i was a teenager, my period was pretty irregular. i was actually put on bc pills to regulate my periods. i was also an athelete and was underweight. have you always had irregular periods? are you underweight? i would sometimes go 8-10 months w/o period. at age 18 i went in for my first gyno visit and they put me on bc pills for regulation. i took levlite for 11+ years and now stopped to try to have a baby. you are at the age that you should probably start to see a gyno. best of luck to you!
Since you are lifting weights and such your body could be reacting to that,If you did not have intercourse then there is a very slight chance that you are pregnant,but if it makes you feel better wait a week and test again and if you get a neg. go to the doc and ask them