Long day in the ER

The spotting I had last night seems to have been a one-off thing, but I then started noticing intermittent tightenings of my uterus. I wasn't sure if they were Braxton-Hicks contractions or what, but I could feel things get really hard in there a few times an hour, lasting a minute or so at a time.
I was pretty freaked out. Couldn't sleep. Finally passed out on the couch around 3:30am after heading out there to read and have a drink so I wouldn't disturb DH. I'd also called L&D to find out what they suggested. Before 20 weeks, I'd have to get assessed in the ER. They suggested I take a hot bath, relax, and see how things went. Well, I wrapped up in a warm comforter, tried to relax, and when I woke up again in the morning, I was still having the tightenings, maybe even more often. Nothing painful or crampy, just weird.
So I woke DH up and told him I was going to head to the ER to be sure things were ok. I wanted to know if my cervix was still long and closed (I'd convinced myself that it felt shorter and softer in the morning than it had last night) and whether the baby was still alive and kicking.
I checked in, the place was almost empty. And then I waited, and waited. 45 min later or so I was called in. Then waited to be seen by a nurse. Then waited 1 1/4 hours to be seen by the doctor. Then waited 2 hours (DH was with me by this time for moral support) to go up for the ultrasound she ordered to ensure things looked ok. And then waited 1 hour for the ultrasound once I was up there (alone in the department).
Thank God things all looked ok. I have a low-riding anterior placenta - only about 1.3cm from the cervical os. The cervix was a little over 4cm, I think. Then she finally showed us the baby (spent a few minutes measuring my cervix before looking at it, which was heart-stopping). It seemed a little sleepy and wasn't moving like crazy, but did have a heart beating away at 141/min, and was growing right on track.
The doc said these must be Braxton-Hicks contractions, and to get worried if there's more bleeding associated with them or if they get painful. Otherwise, I'm supposed to basically ignore them. I'm just happy to have a baseline length for my cervix now, so that I'll know in the future if the contractions are shortening it or not. I was so terrified this morning, I can't even tell you.
She also right at the end said I have some white cells in my urine and that I should take a course of antibiotics just to be safe. I'm going to run out and pick them up now, and then drink more water and relax for the rest of the night.
ETA: Now it's later. I've had a couple more real doozies - 2 within about 10min. I think they may have settled since then. I'll definitely be calling my OB in the morning, and if I'm really freaked, I'll be getting one of the OB/GYNs at the hospital I work at to check me out. Now that I broke the news to my boss (sent him an email Friday, he called this aft to congratulate me), I don't have to hide it. And I'll be making people take it easier on me, I hope.