Thanks for your question - you have already been given an excellent answer by Dr Daniel so I will try to add to this.
Your symptoms do sound suspiciously like piriformis syndrome, where the sciatic nerve is irritated by its close proximity to the piriformis muscle.
In some situations, it can be due to muscle enlargement or entrapment. However, there are other potential diagnoses that must be considered, including
1. This pain might be originating from your spine - such as a disc bulge - in which case an MRI spine might be required.
2. It be a bursitis of the sitting bone (the ischium) and hence when you are sitting/standing you get pain.
3. It could be due to hamstring tightness.
My suggestion would be to be assessed by an MSK/Sports Physician or a physiotherapist who is experienced with these conditions. You can be examined, investigated and treated appropriately.
I hope this helps.
BW
Dr Dinesh
