Hey there! I am not getting the clear picture of your condition with your description. The condition that is being understood by your description is vague.
Try my suggestions and if your condition does not improve, visit a good orthopaedician as at your age a condition like this might involve infective pathology.
Suggestions:
1. Do not stay in a particular position for long.
2. Involve movements like freely walking, slight stretching of body parts at intervals of 2 hours.
3. Change postures every 10 minutes.
4. Take a warm water bath before sleeping or sponge with warm water.
5. Exercises needed to be done early morning which should involve stretching of your body parts. Cat and camel exercise. A sitting cat and camel exercise can also be done during free hours in midst of day.
If the suggestions are followed and you start feeling good, then, Involve movement. The cause is not the sitting material. When you visited the physiotherapist, I hope that the physio checked for spasm and QL muscle spasm, any trigger points. Please check with it. Carry on the instructions if there is no spasm.
Be careful. Any pain or discomfort encountered, visit a good ortho or physio. Your present pain does not seem to be related with your previous one.
Next Steps
please follow the instructions.
Health Tips
Do not worry. Sitting for long durations in a particular position does cause problems.