What Causes Severe Pain In The Groin Area?

I have a pain in my left grone area. This then radiates to my outer thigh and then down to my ankle all at the same time. It prevents me from lying on my left side to sleep. The pain will be constant for 5 minutes or so and then disappear as quickly as it came. The pain can be gone for an hour or two or come back within a few seconds or minutes.No rime or reason for it. I did not pull a muscle at any time. This has been happening for about 3 months.