iPhone keeps rebooting after jailbreak succerssful

hi guys my 3gs keeps rebooting it s started on 4.3.5 and so i downgraded to 4.1 successfully but same issue still reboots. i also jailbreaked it and unlock it but still it will randomly reboot still, at fisrt it did it within 10 mins after successful jb and unlock on 4.1 bb 5.14.02 then i upgraded bb becuz i couldnt unlock the phone on the bb 5.14.02. before i upgraded to ipad bb 6.15 it was rebooting more often , but after upgrade to 6.15 it has only rebooted a few times, it was stable for abit but then all of a sudden it rebooted and i losrt everythign again luckily i did back up the contacts etc, but can anyone help me i hate having to restore all the time, i mean it ok in a way cuz i can always restore it to 4.1 with bb 6.15 and its always unlocked for i do rely on it.

any help would be great thanks guys