preeclampsia

Yes and it happened to me, 3rd pregnancy preeclampsia, HELLP syndrome and emergency c section, my previous pregnancies were fine. Apparently it's rare so my dr wasnt too concerned when I called but said I could go get checked if I wanted for peace of mind, well I got there and it was an emergency with liver enlargement and kidney failure and bp was sky high. I had just seen my dr 2 days before. So if youre having new symptoms, go get checked, even a blood pressure machine at a pharmacy.

You can yes. Headaches are very common especially in the second trimester though. I had headaches pretty much non stop for 7 weeks, but they did go away

Yes. Pre-eclampsia is most common in your first pregnancy, but you can it in subsequent ones even if your BP was normal with your other pregnancies. Could the headaches be due to dehydration or stress? Like you mentioned, 19 weeks seems pretty early.