I came back to running after completely stopping during 2 pregnancies. In fact I completely stopped working out at all. Started back with walks almost as soon as I could after giving birth, and walk/running after getting the clear from my doctor.
A few things that helped me: forgot entirely about distance and just focused on increasing running time, then after awhile, started to look back at how far/fast I was going. I also signed up for a 5k to keep a goal in my line of sight. I just focused on being able to run 3 miles without walking and then after that, I increased distance and speed. Everything also got easier as the running helped me lose some of the baby weight (the rest came off through diet).
Funny part about starting up running post- baby with some extra weight, fellow runners would yell encouragement to me. I found it funny, I only got that when I ran carrying the baby weight