When can i do a pregnancy test?

had last af 28th of october, next af is due around the same time this month,when is the earliest i can test? Hoping this month could be the one..bn having slight cramps lower right side but unsure if its early signs of next af. Only this month I gave up on opk's as I never had a positive, so just bn going by my body really, I know one morning after we bd I noticed a clear stretchy like cm ,not sure what that meant but we bd the following two days also...anyone think its possible this month?