No idea how far along I am

Hi everyone. So I found out I’m pregnant on 16th April but I don’t know how far along I am. I’ve only had 1 cycle since stopping the contraceptive pill and it took me 37 days to get my period and then this was my second cycle but I’ve conceived this cycle so not sure on what the average number of days my cycles are. Do I just go by the date of my last period even though I could be fewer weeks pregnant?

Thanks for your help☺️