Not sure if its even possible...pregnant

Here my problem, i had my tubes tied 2 1/2 yeara ago. My last period was mar 30- Apr 3. I spotted I guess you could call it, none in my panies only saw it when I wiped after using the bathroom and it was only for part of each say from Apr 15-19. (Possible plantation bleedinf maybe) My period was supposed to start may 4. I have me really tires for a couple weeks now at points unable to keep my eyes open no matter how hard I try. Using the bathroom every hour or hour in a half average. Slight headaches more often. Dizziness when I get up to fast. Mild cramping feelings but they don't last to long before they go away but will come back either later or the next day. I took a pregnancy test it said negative. I don't understand what my body is doing. Anyone got any advise or know what might going on or if the rest just might be wrong?