Check engine light keeps coming on

My check engine light has been turning on and off since July now... I do believe it needs a gasket cover job (when the car warms up, it smells like burnt oil)... I keep checking the oil level and it's fine, doesn't go down... check the prestone again, and that's fine. I'm a little strapped for cash these days so I can't afford to bring it to the mecanics right now, but I'd like to know what causes my check engine light to turn on and then off again within a few days (and I haven't fixed anything or changed/added fluids to it)???