What Causes Delayed Periods?

hi my menses have been absent for over 3 months. i had both home pregnancy tests and blood preg. test done, they were all negative. two days ago i started what i thought was my period but only had very light bleeding for one day and nothing since. im starting to feel a little concerned and with no insurance i turned to the web for help. im not sure what to think, whether there may be an actual poblem, or pregnancy.