Please don't fall for any damp 'specialist' offering damp proof injections or tanking.
The source of the damp needs to be found.
In a period property damp is usually caused by inappropriate materials such as cement and gypsum.
I highly recommend looking at the Heritage House website run by Pete Ward.
He offers fantastic advice and the company can come to your house and do a survey regarding what the issues in your home are.
He has lots of videos on You tube and has written a book called The warm, dry home.
No disrespect to builders, but most don't understand damp issues and will just try to cover it up. Speaking from experience!