Q: Please help. Is it worth it

I have a 2001 plymouth neon with aomw problems not sure what is going on. There is bad shaking in the engine mainly while in drive stopped at a light and worse in reverse. Have changed motor mounts and apark plugs and one of the belts. Still need to change the alternator belt wich i believe is the squick im hearing. Let car ait for a week and noticed when i started it alot of smoke came from tue exhaust. Checked oil and was low so put more the whole bottom is also covered in oil. And is pretty black after 3 days. There is a sound from the engine i couldnt describe. And today while driving it sputtered up a hill and did not want to accelerate. Yesterday while driving speed said i was 90 but wasnt moving. And today on the highway it said 70 but did not feel or seem it since cars was passing and honking. Sorry not good at explaining the issues but im not completely sure what problems im looking at. Also not sure if worth fixing. Please help
My car has an automatic transmission.