1998 Fiat Punto Frequent Jolting And Screeching

I've only had my car for 3 months and in the last month it's considerably become more and more un enjoyable to drive. It's not running well anymore, it is frequently jolting when I come off my accelerator pedal and break pedal and it screeches too. It also screeches when I first start the car and sometimes when I'm just rolling or driving. The car has cut out on a roundabout and I had no response from my accelerator pedal and the car had died but engine was still running. Another time my accelerator pedal cut out and I had no response luckily I could roll down a hill I was near and then when I tried to stop my brake pedal locked up so I had to use all my strength in both feet to push the brake pedal down so I could brake. And it jolted so much when I was going straight over on a roundabout I nearly had a car up my bum.

Please help me as I don't know what it is but it has nearly had me killed 3 times!