Maybe Implantation bleeding? Confused...HELP!!!?

Hi! I'm a bit confused...I'm supposed to have had my period today, but haven't. For as long as i've been having them (ages 9-24) i've ALWAYS been on a 28 day schedule. As soon as i was done having my 1st child in 2004, 2 months later, like clockwork, i started my periods again on a 28 day cycle. They ALWAYS come between 2 & 6AM on the morning of. Well its now 10pm and i'm thinking...maybe? Here's why: I've had very sensitive for the past week, some constipation, weird hungery late at night, and some pretty frequent peeing. (LOL...TMI i know, sorry!) Anywho, this afternoon around 2 i went to the bathroom, peed, but when i wiped there was a light pink smear of blood on the paper, but not much at all. I thought, well maybe it's just starting late, so i put in a tampon. I had to pee again around 6, so i took out my tampon and it was CLEAR!!! i decided to put in a new one just in case, and i just changed it and it was clear too. This has NEVER happened before! Could that little blood smear have been implantaion bleeding? I don't have any cramps or nausea like i usually do with my period. No bloating either. Can anybody help me out? What's going on? Oh and by the way, i'm only 24, so i don't think its time for my cycle to change, so...what's going on?! Thanks for any help!