Is the burning the same in both your legs?
Where exactly is the problem?
There are a few significant causes for this but in a 26 year-old woman with normal blood tests the chance of this being true in your case is not , at all , high.
To be honest I would rest up and expect the problem to settle down - sure if you are no better in 2-3 weeks get back to your own Dr - but for now I would not be worried.
Myositis would need to be considered ( but your normal CPK is NOT consistent)- also spinal cord disease if the pain is in the back of your thighs and your physical exam was abnormal.