Negative pregnancy test....tested too early??!?

My LMP was on 4/10/2009 my cycles normally run 32 to 33 days every month. I have been off of birth control for several months now due to it causing high blood pressure. The other day i was looking on a site and it had an ovulation calculator. I've never seen one, my previous pregnancies were all unplanned & i don't really pay attention to when i'm supposed to ovulate and stuff so out of curiousity i looked at it and during the time i was "supposed" to ovulate i had like every other day with my boyfriend. I didn't think anything of it cuz we have been having unprotected for a long time and i haven't gotten pregnant. however my period was supposed to start today on 5/13/2009 and it didn't. This probably doesn't seem like a big deal but normally the day before my period i have severe cramps, nausea, stomachaches, headache, irritable, and than my period is there when i wake up the next morning but i had none of that this time. I took a pregnancy test but it was negative but i'm wondering if it could have just possibly been to early and i may still be pregnant? With my other children i didn't know i was pregnant until i was almost 2 months along because i didn't really keep track of my periods and so i only knew because i get really severe morning sickness and would start getting sick. Is it possible that my body just don't produce enough hormone until i'm that far along to show up on a urine test? should i wait and try again or is it safe to say i'm not pregnant and period is just pulling an unusual late appearance??