Changing of due date

Hi po, ask ko lng bkit everytime nagpapa ultrasound ako iba iba ung weeks old at due date na lumalabas? First ultrasound ko nung feb.2019 8 weeks aog: Sept. 27 due date. Nxt nung May 19 weeks aog walang DOD nkalagay. Nxt was aug. 9, 31 weeks and 1 day. Pero pag nag base ako sa first ultrasound that day ng aug. 9 dapat 33 weeks n sya. So nag pa ultrasound ako ulet last aug. 20 , 32 weeks and 6 days nmn lumabas and oct. 9 na due date ko. Hndi ko tuloy malaman kelan ako mag leleave sa work. Any advise po? Thanks in advance