Advice please!

Hi everyone, I'm 21 years old and ttc my first baby. I've been taking folic acid and getting plenty of exercise as well as maintaining a relatively healthy diet. My periods are always on time, like almost down to the exact hour every month. So tomorrow it is due to start, yesterday I took a hpt, just a £1 pack from ASDA with pink dye and it was BFN. Today I have woke up to lower back pain and very light pink discharge only when I wipe. I thought AF was starting a day early so put a pad on but there's never anything on it. It's quite a creamy consistency (tmi I know) and I'm just wondering if anyone has experienced this..is it just AF coming or is it poss pregnancy? I'm probably clinging on to any form of hope but your stories and opinions would be appreciated. AF normally comes on bright red and more heavy for me and generally lasts about 4-5 days, don't remember experiencing this before. Thanks ladies :)