Can you give a bit more info? When you say you can't go and haven't been for a while, do you mean there has really been no urine at all? When did you last pass anything?
I don't want to scaremonger, but urinary retention can quickly become a serious medical emergency. If you can't pass anything despite being well hydrated then I would recommend you seek medical advice as soon as possible. Even a dehydrated person has a minimal amount of urine production and your bladder will continue to fill, so the sooner you act, the better.
Please let us know what you do.