I have always done gentle running/jogging (never been fast or amazing!!). I ran up until 21 weeks, and actually found that if I felt a bit nauseous it was great to get outside and get some wind in my face. Just got to bite the bullet and make yourself go (probably no different to not being pregnant!) I also changed from enjoying running in the morning to preferring to go in the evenings. I only gave it up because of the hot weather during Feb. Probably would have run longer if it had of been cooler.
The most important things are making sure that your body isn't overheating, and heart rate is a good indicator of that. I tried to keep my heart rate at or below 150, only going up to 160 or 170 for short spurts. Running intervals with walking in between is one way to do this if you struggle to keep your heart rate down. Don't wear too many layers of clothes. Keep hydrated and keep up the pelvic floor exercises too.
You are preparing your body for a really physical event (birth) so stay as fit as you can.