Volvo S40 II 2.0D power loss on the motorway

Mf all of you can’t count on it. I’m new in this forum and for over two months proud owner of a Volvo S40 II 2.0D momentum. I’m very happy with the car, especially because I got it far below the usual price and the car is wonderfully preserved, outside as well as inside no damage and like new. Unfortunately I have been having a problem for a good three days when I’m on the highway. I drive on the highway in 5th gear, under 2.900/U min (are about 120/kmh) the car has as good as no power. I can’t really speed up and as soon as a small slope is there, it’s over anyway and the car is only slower. Of course I’m not sure whether this is normal with a Volvo or not. I can’t imagine it now because it wasn’t that bad a few weeks ago. I didn’t drive a lot on the highway but still don’t freak me out that it was just better/others before. Even in the 4.Gang I’s more the feeling that the car isn’t running like in the first few weeks, but I can’t expect to get a lot of a lot of it.