renault clio - 2003 1.2 power problems

hi, new to the forums as i don't know what else to do with my car. (renault clio 2003 1.2 - 3 door)

had my car serviced about 2 months ago where i replaced the H T leads, spark plugs, oil ECT. recently my car hasn't got the power it use to it takes forever to got up to 20-30 mph and going on a motorway i cannot get passed 60mph if its a little hill, i have to lower the gear to keep it at 60 otherwise it just drops the speed.

main problem is getting off its rattles the car a lot like it is misfiring which i had problems with before and they fix this in the service but it has gotten worse than it was, i took it to a garage again and he said it could be the coil pack as the service wasn't long done i left it with them and got a call and said he hasn't changed it as he was 80% sure it was the head gasket going and was going to be £500 odd to fix.

i brought some 'real seal' that goes through the water and fixes head gasket. however this did not fix the car power problems and now stuck on what it is. the garage said the cylinders are not getting enough pressure.

i still drive it at the moment as all i have to do is rev more. but today going home from work the check engine light kept flashing and then the light went off (this happened 3 times over a 20 min drive)

i have got my MOT in 19 days aswell would this fail as i don't have the money to buy a new car at the moment
any ideas or any similar experiences would be a big help

thanks

renault clio - 2003 1.2 power problems