What Causes Delay In Periods, Nausea, Cramping And Diarrhea?

i think i may be pregnant. i took a test and it was negative. however ive gotten extremely nauseous in the last week, cramping slightly in my lower abdomen, diharrea, tired and hungry all the time, but some foods make me want to puke, i havent puked yet, but it seems i get real sick at around 6 or 7 at night. my last full period was on april 15th, and i had another one i guess on may 14th thru 17th which the length was unsual for me because my period normally lasts for 8 days at least. also, i just had spotting on the 1st day, then it was heavyish for 2 days, and then stopped completely on the 3rd day then started again and just trickled down to nothing by the 17th. very odd for me. please give me your thoughts, i am nervous.