I was regularly running 6 miles every other day since I found out I was pregnant. I was doing a much more intense schedule before that, so the 6 miles was pretty easy for me. I did run into a couple random days starting around 10 weeks where I felt like I could barely run 1 mile, but then I'd be feeling great again the next time. I think it's normal to have energy swings.
I just started a new "schedule" of 4 miles most days of the week because it seems to help my overall energy throughout the day to get some miles in. I ran my entire first pregnancy. You just have to go with how you feel every day and make adjustments along the way. No expectations - just do what feels good.