What do you mean with D8-D9 Thoracic I assume. otherwise I am completely confused.
In case you have manipulated thoracic. What have you maipulated; the vertebraes T8_T9 or Costa T8- Vertebra T8 -T9?
What I try to point out is that it is easily done. Anyhow what sort of pain are you talking about, sharp? dull? burning? Does it radiate? Whereto? Contuous pain? Why did you choose manipulation?
Diff diagnose; blockade of joints? Triggerpoint(s)? (referred pain in which area?)
referred pain does it go towards the front (from medial more lateral or from cranial to dorsal?
Palpation where does it hurt.
I think the reason for the immediate return is that you do not solve the problem. In case of p.e. a triggerpoint in a muscle the muscle might relax for a short time or alike but comes back immediately.
The way forward is to find the triggering factor and then start your treament. Be aware that there might be several triggerpoints in the area so look at a `map`ala travell and show it to your patient. You can try acupressure / US but to my experience the best is acupuncture in these cases.
By the way 3sittings with manipulation?