Well the second trimester was a bit of a roller coaster for me. It started out great. First trimester I felt so slow, sluggish, and had difficulty breathing. My pace actually picked up second trimester! And the breathing difficulties went away (except of course for whenever I climbed stairs).
From weeks 17-22 I was running consistently and actually felt really good. And then week 22 hit. I don't know what happened, but I got hit with a ton of bricks. All of a sudden my runs got really uncomfortable. Pelvic pain when running, sciatica, back pain all the time. My 11:30 pace dropped to closer to 14/15 as I interspersed walking in with my weekday runs.
After about 2 weeks though, my pain disappeared. My runs became comfortable again and my pace went back up.
So why? What happened? I have no idea. Maybe taking it easy for 2 weeks was what my body needed. It's so important to listen to your body, especially when pregnant. Of course, my return to "fitness" coincided with my busiest time at work. So second trimester I felt better and ran faster. But of course, had less time to do it.
I'm really looking forward to my third trimester running. I've got a couple races lined up and have already started back in on my longer runs. Yesterday I even managed a couple of sub-11 minute miles!