the test says no, but i'm thinking ... maybe?

As a rule, I am on a 28 day cycle. As of today I will be 3 days late. I have no signs of getting my period (cramps, breaking out, bloating, discharge). I have had other symptoms the past couple days: slight nausea, constipation, slightly tender breasts, feeling thirsty, mild headache... I took a pregnancy test this morning, which expires this April, and it gave me a negative response. Needless to say I am very anxious to find out what is happening to my very confused body. Should I take another test in a few days, or see a doctor? If anyone has an answer or some advice I would loooove to hear it!