Ok, I wanted to confirm I knew which aspect of the upper leg it seemed to be coming from. When you said it moved to the groin, I was not sure if it started in a different area first.
When the pain comes from the groin area, this can indicate a problem in the hip joint itself. This can also be due to tendonitis. Hip pain can also cause referred pain down the leg.
If you have tenderness when pushing on the groin area, this would be more indicative of a strain or tendonitis that would have been brought on by the increased activity you have done recently.
Treatment includes rest, ice, anti-inflammatories for a few days.
If this does not help, you should see your doctor for an exam and an xray of the hip.
Other possibilities include a pinched nerve in the back, a hernia in the groin, bursitis of the hip (this is a common cause of pain on the outside of the hip area, and commonly causes pain that is worse at night as well--I will include a link so that you can read more about this. It does not usually cause groin pain, though).http://www.buzzle.com/articles/trochanteric-bursitis-exercises.html
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