We all will get a screwy period here and there specially as we get older..i know when i first got my period at 13...they would last a full 7 days...now since i had my son in 2003 they last 4-5 days if im lucky, usually the first 2 days is heavy and the rest is the light brownish ,like you described. and sometimes even a barely there color.
Brown blood is old blood so it's hard to know what is going on. You could still take a test if you wanted to but chances are that was your period and maybe next cycle it will be more normal for you!