Woke up with pain back of left thigh been there for two days any help no swelling or discoloration?

Probable strain: Most often in these situations you have done something to strain a muscle but don't remember exactly what activity might have caused it. Gentle stretching is a good idea, and icing it using Ziploc bag of crushed ice or a bag of frozen peas for 20 minutes two to three times a day. I would give it a couple of more days, and if it persists would considering calling your primary care provider.

Several options: Pinched nerves in your lower back, muscle strains, and less likely blood clots could cause these symptoms. Try ibuprofen and acetaminophen, and if that is not helping you should see a physician to be evaluated.

Need more info: In a 28 y/o male, muscle pain in the posterior thigh is most likely trauma related or exercise related.