When am I due?

I should have got my period on the 29th. 4 different apps are giving me 4 different due dates, some say 4 weeks 3 days, some say 5 weeks, etc. I don’t know what my cycle is because thankfully I fell pregnant on my first cycle coming off BC. I know i won’t know for a long time, here in the UK we don’t have a dating scan until 12-14 weeks 😱