Any long distance runners (4+ miles per run)?

rockychryslerb2010

I am almost 6 months pp and started running again around 3 months pp.  For the first 2.5 months, I kept my runs under 3 miles (with a 5K here and there), but lately I am starting to build up my milage to race in Tough Mudder and a Half Marathon in the fall.  I am only adding about .25 or .5 miles per week to increase, and a little over a week ago did 4.5 miles.  The next day, I noticed some pain in my left side by my incision.  It isn't super painful, but it is at time uncomfortable.  DH and I also had particularly feisty sex that night, so I'm not sure if it is the running or the sex that caused the discomfort.  I cut back my milage for the runs and said I would give myself a week and then call my OB if I was still feeling it.  

Well, today is one week and I still feel it.   I EBF and haven't gotten AF yet, so I thought maybe I was getting it and that was the pain, but I never had discomfort like this for so long before AF actually showed up.  I know I should call my doctor, but has anyone else experienced something similar when increasing distance?  I think it is weird that I felt fine when I first started out, and now almost three months later I have pain.