What's going on with me????!?

Ok, so my period was supposed to come on december 13, it hasn't come yet. I'm extremely regular (24 days, like clockwork). I'm also more tired than usual. And snap at silly things. I went to the doc today and they took a urine test and tested it for pregnancy, and my doctor said it was the "wimpiest positive she's ever seen". I also took a test at home, and it came out negative. and so i took another one and it was not conclusive i guess. So i just wanna know what the heck is going on with me. If anyone can tell me anything it'd be so helpful. Thank You! :)