Missing or delayed period

I haven't seen my red ninja since July. (I remember cos I was very happy to not have to deal with it on the 4th.) It's now the end of August/Beginning of September, and I haven't seen it. I'm used to my period being delayed, but it's been delayed longer than usual. I usually only have to wait an additional month, and BAM, there it is. It's been almost two months, and I'm getting a little worried. I know that I can't be pregnant, because I'm not sexually active. I've only recently gone to third base, but nothing more, and my period was late before that. I have a slight discharge, but it's happened before, and my period would be right around the corner, and then everything would be fine. Now... I just don't know. My appetite's been wonky, as has my sleep schedule, and I'm pretty sure I'm stressed - my second year of college just started, along with my very first "real" job. I sometimes get like I'm PMS-ing, and my breasts are finally sore, so I'm thinking I may be worrying for nothing, cos the ninja could be lurking just around the corner, but I wanna know just to be sure... I was in England over the summer, and only returned to Florida in the middle of July. I don't know if all of the traveling I did right before school started, and the fact that maybe I haven't had a chance to rest is what's going on, or if it's maybe a hormonal imbalance like my friend found out she had a few weeks ago... She's telling me to go see an OB GYN and I'll prolly get put on the pill, and I'm planning on going and seeing one as soon as I can - I'm just so busy, I never seem to have a chance. Before I do go, do you have any idea what could be wrong with me?