Hi Cerah,
Apart from the tongue, I'm not sure you've seen any improvements in this dog. Have you? If you have, then we can pursue related formulas for the prostatitis itself. Hydrangea and Eupatorium is doing a nice job of managing one case for us right now (asymptomatic on it).
Damp Heat leads to Blood stasis. If the dog is at that point, then Ge Xia Zhu Yu Tang may help. Or Pang Guang Zhu Yu Tang (Dispel Stasis from the Bladder Decoction) from Kan Herbs.
If nettles helps in general, then nettles root may give you some prostate benefits.
Those are my thoughts. Hope they help,
Steve