hip pain

I am a 40 year old woman in good health and exercise about 3-4 times per week on a treadmill or elliptical for 30 minutes and then weights. On Monday of this week, after walking at a 4 incline on the treadmill, I began to notice throughout the day a sorenesss in my hip bone that felt much like a bruise but no bruising. It still feels that way 3 days later and mostly when I walk–not when I sit, lie down or sleep.
Is this anything to be worried about?