confused

Hello po.. Buntis po acu and im 19 weeks pregnant according xa rural health center nmin.. But im confused kc po irrwgukar po ang period cu. And last menstrual cu is january 30-feb 7 2019. But then before january na period cu 3months dn po acung nadelay.. July 12 pa po ulit blik cu xa center para humingi ng ultradound request. . Accurate po ba if kahit irrgular ka xa period kung kelan last period mu dun ka din magstart mag count?? Confused po tlga acu.