I have also had costochondritis a few times and it is certainly painful. You seem to be having a prolonged case, and because of that I would suggest asking your rheumatologist to check you for any possible related inflammatory conditions, especially if you have chronic back pain or frequent joint pains. A few simple blood tests can be done to check inflammatory markers and anything else that might be related. Ultrasound is not usually done as a diagnostic test, especially since you had a CT scan. Anti inflammatory medication, heat and avoidance of aggravating activities like weight lifting usually help. Some physical therapists use ultrasound for treatment and you might explore that option. I would also try diclofenac gel rubbed over the area twice daily. It’s over the counter and works well when the inflamed joints are small and close to the surface. I hope you get relief and it goes away for good.