How much swelling is too much?

How much swelling on your feet and legs is normal before asking about preeclampsia? I have a notoriously low BP and always have but now my systolic is in pre-hypertension and my diastolic is getting there. My doctor said that if I don't have hypertension there's no reason to check or be concerned, and I believe her!! But my feet ache and they're so purple and it was my day off! I drank water and relaxed!