Suggest Treatment For Symptoms Of Runner's Colitis

Question : I am a healthy, 33 year old female, with 2 children, youngest being 9 months. I've been a runner for years without any significant stomach issues. Following the birth of my youngest child, I resumed running and began having stomach cramps at the end of runs (usually about 6 miles), followed by diarrhea. It usually happens 1x and then stops. Doesn't occur every time I run, and I started hydrating more, which really seemed to help diminish effects. On Christmas, I went for a run, realized I was quite dehydrated at the start and it was very unusually warm and humid. I came back, had some diarrhea and it had a relatively small amount of bright red blood. Was very scary to see and the following Monday, saw my PCP. She did an exam, said no hemorrhoids or an obvious fissure, but it might have healed as it had been a few days. Tested for current blood and said none present. She doesn't recommend a colonoscopy at this time, but if it occurs again I should get one. Having no clear answer is scary to me and I wonder if I should get one? I also wonder if there is a chance I'm dealing with runners colitis, but obvious the idea of something more serious is scary!