Late period

So I have a really irregular period, and before I got a boyfriend I didn't even track it because there was no point. But now I have to be careful because we are having sex and I don't want an accidental pregnancy. We use condoms, and he pulls out way in advance but I'm 10 days late on my period. I've been taking pregnancy tests but they have come back negative. Is it possible that I'm not actually late and what I thought I was tracking as my 'normal period cycle' wasn't my normal cycle of 25 days? Maybe it's longer? Or maybe those pregnancy tests were false? =_= I am obviously very worried here!!! Perhaps stress is making me late?

I have also been experiencing a yeast infection for like 4 days now, so I'm not sure if that contributed anything?