How Does One Confirm Pregnancy ?

29 year old healthy female missed period, spotting, negative pregnancy test I m 29 years old & otherwise very healthy. I don t take birth control & we aren t being safe, just letting nature take it s course if you will. I should have started my period on 5/12 so i took a test on 5/17 but the next day started what I thought was going to be my period. It started out pinkish on the toilet tissue then changed to brown by the next time I went to the restroom. This lasted for 2&1/2 days but was only enough in quantity to have only filled one tampon(don t worry I didn t only use one tampon over 3 days). I took another test yesterday, 5/25, which was negative again b/c I m now experiancing nausea , slight lower abdominal cramping(tightening), am extremely tired & an increased sense of smell. Could I be pregnant? Should I go for a blood test?