T.W.
As long as you are keeping up with your bodies caloric needs, you should be fine. While nursing, I ran and trained for races, did some intense workouts weekly and did not have a problem with it affecting my milk supply. I also never had a problem with the baby rejecting my milk due to lactic acid buildup. (I was told this could be a problem)
Just get a good sports bra and remember to go easy when you get back into it.