Spotting instead of period?

So I lost my virginity abut a month and a half ago and I have not had since then. My first period after that was just spotting so I took a pregnancy test after a few days and it came back negative. I have had 2 more cycles of spotting since then and it is brown and only lasts a few days. Should I take another pregnancy test or is it something else? I'm also studying abroad in England right now and it would be difficult for me to get to a doctor. I have also been traveling a lot every weekend and have been somewhat stressed about school so that could possibly be related. I was on birth control from last January until July but I have not been on it since then. Any idea what is going on? Thanks!