99 Pontiac driving me CRAZY! What should i do!??

I have a 99 pontiac grand prix GT w/140,000 miles. I have the title & have replaced just about everything the axle tire rods brakes rotors coolant bin motor mounts the list goes on and on. I love the car because it is my first car but I'm pregnant and now it needs struts shocks more motor mounts and fuel injectors. The service engine light is on but with the baby on the way I don't have much extra money to throw away into repairs. I'm only 18, am unable to get my DL due to TX law that allows them to charge surcharge fees when you get a ticket. So I owe DPS $5,000. I have insurance and want to sell this car. I want something dependable for my child, should I put more money into it or sell it while i can before it's a hunk of junk and get something else?? There are 2 car dealerships that are willing to work with me but my monthly payments will be $300-$400 a month for a USED car price $11k-$14k. Should I spend more on my car or jus get rid of it and use the money for down pay!?? PLS HELP