Please help. (Tmi)

I've been thinking I could be pregnant but i got my period on Monday which was right on time. It wasn't like my normal period though it's been much lighter and it's been very spotty. I was supposed to be off on Thursday but am still spotting. I can go all day without spotting then just randomly start again. I took a hpt on Monday but it came back negative. Is it still possible that I'm pregnant? A friend of mine is currently expecting and had multiple negative hpt before she got the positive. If so when she I try and retest?