2003 Range Rover violent jerking + check engine light

I have a 2003 Range Rover HSE and very recently my car has been jerking and 'shivering' violently at speeds of 1st gear and often whilst driving at steady speeds and even accelerating. Acceleration has been sluggish lately. Just now I tried to force it to accelerate whilst jerking and the Amber Check Engine light came on and started to blink. I am extremely worried and agitated right now and I don't know what to do. Please help me here. Thank you very much!