Early period which starts and stop - infection?

Ok my period is usually very regular. It comes once a month and it would last about 5 or 6 days, with the first two or three days being the more heavy flow days. However, I had a really really light period three days ago. It started with looking very light red and sometimes a little brown. But it didn't grow heavier and it actually stopped by now. In fact, it turned brown when I look on the pad I was wearing. I'm actually supposed to get my period next week, so this is actually a week early, but why does it start and stop? And why did it turn brown? Do I have an infection? If I do, are infections like this severe? I am not sexually active and I am not on birth control pills. I'm 18 years old at the moment.

It has never happened to me before. Is this normal? Has anyone had the same experience?

Thanks in advance.