Was due on 23rd March, but now 4 days late and NEG preg test

Me and my partner are trying to conceive and have been trying for around 10 months now, I was due for my period on monday 23rd but I had a slight show instead, then it stopped, now my period hasn't come at all. I have done 2 tests and both come up with negative. I have been feeling sick and getting cramps and really really thirsty (dunno if this is anything to do with pregnancy but I am getting this alot) Really haven't got a clue what is going on at the moment...any ideas? Thanks