late period

I am 10 days late for my period today. I've taken 4 pregnancy tests over the past 3 days and all have come up negative. I have had some of my normal pms symptoms mood swings breakout and tender breasts but no cramps or anything which I'm prone to. I'm in a new relationship and have been having a lot of sex averaging twice a day but this is the only change in my life I can think of. Help!! Has anyone else experienced anything like this? any advice would be helpful!!