Have you increased your mileage? If so, how fast? Most experts recommend only increasing about 10% per week. Most new riders tend to increase a lot faster than that if they're enjoying riding. If you start with 5 miles, a 10% increase is only 5.5 miles, not much. I'd be more likely to do 5 miles, then 10 miles, a 100% increase! Sometimes it just takes cutting back on mileage a bit to get used to a new bike/position. Other times there's a saddle or fit issue. Unfortunately, this is very hard to diagnose over the internet!
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow