Hemmorhoids are bulging veins from your rectum that protrude through your anus. You can have more than one unfortunately. So even if you had one removed prior to pregnancy, you can still get them again (there are many veins down there). They do get worse and/or present themselves in pregnancy since you have a large amount of weight (baby, placenta, amniotic fluid, uterus, etc.) putting pressure on everything below (rectum, anus, vulva, legs). All you can do during pregnancy is to try to relieve the discomfort, but they will not go away during pregnancy (most recede after delivery at some point). You can do sitz baths, witch hazel (Tucks) pads, hemorrhoid ointments (with approval by your OB), colace (stool softener), increase fluid intake, increase fiber intake. If you are having too much pain, then you should see your OB-GYN ASAP & may have to be referred to a gastroenterolist or general surgeon for other options.
Hope you feel better soon!