ovulation testing strips

Just got ovulation test strips in the mail and I started my period on the 2nd of this month...we are trying for our second baby..we got pregnant the first month with our son, but this time is taking a little longer has been about 4 months..when should I start taking the test? My cycle hasn't been consistent it's all over the place like one month it'll be 28 days and this month it was 31 days until I got my period so I'm not sure when to start taking the ovulation test