Damp?! Help!!

We have had an extension done on our 1930s house last year. The whole house has been renovated and decorated inside also. Just as we're about to move back in and we've discovered damp patches in the lounge and the hall. They are just above the skirting boards by the fire place, around a light socket and on an internal wall behind the sofa. There is also a larger on on the inside of an external wall (this was the first one we noticed and had some external work to a drain and to the pointing which we thought would solve if).

Does this sound like rising damp? Could it be condensation and needs us living in the house to sort it and dry out?

Advice very welcome!

Are you sure it is damp & not black mould, some pics would help.

Not rising damp,. by a fireplace it will be falling damp, down he chimney, has it been capped and ventilated?.

I don't have any pictures to hand and as am not living in the house at the moment. But it's definitely damp. It's not only by the fire place it's in several random locations which include both internal walls and external walls.

How long since it's had any plastering work?
Damp behind furniture suggests poor ventilation, have any vents been sealed.?