I think my due date is wrong

So let me start by saying I had my period two times in December. December 4-7 and December 24-28. I had a feeling all January that I was pregnant and started feeling sick around january 25th and found out I was pregnant on feb 3rd. The ultrasound seems to match up with the December 24th period well as I get further along I feel like im further then it says. I'm 27weeks and have been feeling movement since week 17. My daughter was only 7 months when I got pregnant. My daughter was really small so i didn't feel her movements as much as him. But lately I've  been feeling  some pain in my lower belly, some pressure and I feel like maybe he's dropped. Here's a pic of me from a few days ago. Do you think my due date is wrong and I'm actually 2 weeks farther along? Has anyone else gone through something similar?