23 days late..HELP ME!!

I need some advice... my period is 23 days late and I've taken a home pregnancy test and the hospital pre test and both came back negative. this morning I woke up and my nipples hurt like they were cold...but I'm in 80 degree weather. I can't sleep until 3am and force myself to wake up at least by 12pm... my next period is supposed to come in a week or 2 and the last I had sex was early September before i flew across the country... can anyone give me any word of advice, hints, common events or what you think is the problem..?