What Causes Delay In Menstruation Other Than Pregnancy?

Hello,
i just need to know some answers about pregnancy.
i resently have been feeling very sick, feeling like im gonna vomit, but it doesent always come up, sore nipples. alot of cramping. back pain, i missed my period also, it was due 7 days, that is so strange, cause i never miss a period, i was havin alot of unprotected sex with my boyfriend :/ and ever sence then i started feeling diffrent, and thats when i missed my period. i went for a blood test 2 days ago, but they told me i wasent pregnant, but they never told me what was going on? they just said sorry. well i still belive i am pregnant, help?