PLEASE HELP! what should i do? i'm not sure if i'm pregnant?

ok... i am Rh negative as i found out in my last pregnancy... i lost the baby and i dont want that to happen again... i thought my period was due about 3 or 4 days ago.... so i took a pregnancy test and it came back negative... well then today i started spotting lightly a light brownish pinkish color... i am not sure if the last test could have been wrong and i should retest or i just am paranoid about losing another baby... what should i do? Please help!