Pain in left abdominal area

I've been going to the gym for about a month now, and run 2.5-3.5 miles about five times a week. I don't lift any weights or do sit-ups. Yesterday I noticed a dull but intense ache in my left abdominal area during the first five minutes of my run. Yesterday and today it has been noticeable when sitting up, walking, etc but it was fine during my run today. It's only my left abdominal area, and its very low, almost right above my vaginal area. I thought it could be a hernia, but it didn't bother me during my workout today and I don't lift weights. Thoughts?