Engine Noise and Slow Driving

I have a 2000 Dodge Neon, the car my parents bought me in high school. I have generally tried to take good care of it, but it’s had a rough life–sitting at home in NC for my first two years of college in NJ, not being driven much. After this summer sitting in my college parking lot while I was abroad, some girlfriends and I went on a dinner outing and I noticed the check engine light was on. The next time I took the car out I put in two full quart bottles of oil (eek!) but the light didn’t go off. Then the car started making more noises than it used to (before I drove it up to NJ my mechanic said something about cans and it cost me $400, and still made noise). The noise is a sort of grrring and clunking sound. Then it started doing this thing after I make a stop, where it takes a while to get driving again. Even though I push on the gas, it goes very slow, then makes a few click/clunk noises and finally will drive. If I slow down or brake again, it again takes a while for it to start driving right. Please tell me this isn’t a billion dollar problem that’s going to eat up my spring tuition money!!