Im a 20 year old male 165lbs. Im not new to endurance events, I come from running half, full marathons and swim pretty regularly. I'd consider my self in very good shape I run my half marathons at a 6:35 pace. Im new to road biking, as in this week, my dad in his 40's has been biking for 5 years or so now and is in great shape. I went on my first ride with him the other day had a major side stitch and stopped to relive it, I couldn't finish the ride the pain started about 30min in about 8 miles and its the worst side stitch I have ever had. I then went out again the next day for an hour doing 15 miles and had no issues at all. Today went out and same old story as first day. What do you guys think it could be, just need to get into biking slowly... Im a little stumped I dont think its a lack of O2 because my legs arent cramping and feel fine. Tell me what you guys think any thing could help at this point.