Why are my legs (middle half towards my ankles) hurt and a little swollen?

These past couple days my legs, the middle half down to my ankles, hurt when I walk alot or stand to long. Today I notice they might be a little swollen. I know that pregnant women can get this and it's common. But when I googled, a couple sites mentioned preeclampsia, which after reading mde me worry. How do you know you have this or just regular swelling? It says "woman is diagnosed with preeclampsia if she has high blood pressure and protein in her urine after 20 weeks of pregnancy." I'm sure I don't have high blood pressure and protein in my urine because my doctor checks this and never says anything. But I am only 19 weeks. Should I be worrying?