Timing contractions

At what point did you start timing contractions? I've been having BH frequently for over a week but with no discomfort. Lately my back feels sore and I'll have cramps along with my belly getting really hard. I'm a ftm so I'm not really sure what to look for. Should I start timing what I'm feeling and see if it becomes more frequent? I'm 38 +2 so I know it may just be something that comes and goes.