1999 Pontiac Sunfire Knocking sound in engine

I'm trying to get my 99Sunfire Gt 2.4 back on the road, knowing that it has sat for a year (due to water pump needed changing, which we did change). We have put a lot of work into it but it seemed to have no juice!!! Very bogged down feeling, so we changed the catalytic converter and some muffler parts thinking that was for sure the plugged up feeling, but "no" now it sounds worse! there is some kind of knocking in the engine that now we can't drive it. we did a oil change and took it for a run, and the knocking got louder and when we checked the oil, there was little to none, so we are not sure if this is a "major" engine repair or something like a sticky valve (i did read that somewhere) please if you could give us any advice I would really appreciate it. Don't know what to do now. Thank you

Shelly Michaud