As a test, use your good leg to act as some resistance as your bring the sore hamstring back to the buttocks.

If that feels "good" in a good way, then do that to coax along the hamstring. Sounds like you might have a muscle imbalance.

I'm not a PT or anything... I would not use pain killers to mask what's going on there until it did clear up or until you get a medical diagnosis. Don't be sitting on it, etc.

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Indoor Triathlete - I thought I was right, until I realized I was wrong.

I wouldn't do anything for 24-48 hours. Just rest...walk easy. See how it feels as the weekend progresses. If its getting better, then play it by ear until it feels good enough to maybe try some easy biking. If it isn't getting better or you have bruising in your leg in the area where it hurts....then call a doctor and get it looked at. I'd guess you'll know one way or the other by Monday.

I wouldn't run until you don't feel any discomfort at all. And then I'd return to running pretty slowly, when I did start back up. That might be a week or two..assuming it doesn't require any special treatment.

I'd stay away from swimming, also....as walls especially can be pretty stressful on the hamstrings, AND can cause muscle spasms in the hamstrings when they already fatigued, overworked, or overstimulated.

ETA: don't do anything that makes it hurt. But, my personal experience is that sitting still is worse than light activity (like walking easy). Easy rythmic movements always seem more helpful than absolute rest, as long as they dont cause pain.