Ipod touch earphones only working in one side?

I decided to listen to my ipod one day and realised that the headphone socket only works firmly in one ear (the right one) it does slightly work on the left but you have to wriggle the jack around and the slightest touch will knock it off. I was jailbroken at the time so i restored to unjailbreak and i still have the same problem, i have an ipod touch 2g on 4.2.1, Help to fix this would be very appreciated :-)