guys can anyone help my fiat 2003 1.2

When i leave my car for a long period of time say overnight, i start her up and she shakes and vibrates like mad, then takes a while to build up speed and bunny hops when im going along, a real lack of power and i noticed today im hearing little bangs to! i had the engine managment light flashing in amber this morning. I have had spark plugs in 4 months ago but i was told they need to be fiat spark plugs or a problem could arise, hope anyone can shed some light

#1 Stop using it before you cause some serious damage.

At night spray the plug leads with a water mist. If you see any sparks replace the plug leads. Also look for air leaks into the inlet manifold as they might affect fuel mixture control.

Compression test for blown head gasket
Cam belt - check for stripped teeth

After that you need to interrogate the ECU fault codes.