Glow plug warning light limp mode low fuel pressure?

My 13plate 1.6deisel keeps jumping to limp mode soon as engine has to deliver power : up hill or overtaking which is now impossible !!! Fault code is low fuel pressure main dealer says wrong fuel filter so changed to there filter £45 no change still jumping to limp mode now engine warning warning light on also now dpf light on and seek owners handbook ??? Whats is goingon please any ideas ???? Many thanks -parkways!!!!