please help

I am so new at this, I have a question and I have been self diagnosing myself for the past 4 days by looking things up online.. OK well here goes.. My period is 8 days late and my vag smells different.. A weird different, and my nipples burn. I researched online and it could be one of 4 things (or so I have read) pregnancy, menopause, STD or Yeast infection. I took a pregnancy test and it came back negative and I'm only 21 not old enough for menopause. My partner and I both are clear of STDs and I know Its not a yeast infection because I have had so many that I know what it feels like. No it doesn't hurt to pee and nothing itches. But I also get like a weird light crampy feeling lower on my abdomen than I normally do.. I was wondering if anyone has had similar experiences and would be willing to share what it was and what I can do?