What Causes Late In Period With Frequent Urination, Bloating And Headache?

hi, im wondering what could be wrong with me?
my period is now exactly a month late i havent had it since december 16th 2010, i am sexualy active and my husband and i have been trying to conceive since march 2010 with no luck. latley ive had frequent urination, bad head aches which i never used to have i eat more im bloated and i am always tired and again missed my period.. ive taken a 3 pregnancy tests but theyve a;; turned out negitive, what might be happening?