Go to your doctor, they will probably be in awe of you for training for such an event and will not consider it as being bothered at all.
I had a similar pain on the inside of my right shin, I put off going to the doctor for two weeks and when I eventually saw him, I was congratulated on being so active and told that I had really severe shin splints and was using the wrong running shoes.
Never be afraid of seeing your doctor if you have a sports injury, even is you think it's minor.