peugeot 206 loss of power and engine shaking?

Hi i have a 206 02 plate. have had loads of problems since i got it a yr ago but basically we fitted a new coil pack a few weeks ago because car would start n kept cutting out every 10 mins. after that the the engine seem to change it went loud n didnt have much power. I havnt driven it for 4 weeks now as my bf's dad has been repairing it n has fitted a new cat convertor as we thought it could of been something to do with that. car now runs n doesnt cut out but is loud n shaking wanting to stall. Feels like no power wotsoever :(, we really dont have a clue wot else it could be causing this. i cant drive the car anymore as it has now become dangerously sliw HELP! Thanks