I think you should listen to your body, if you're feeling dehydrated, you probably are. Typically I read that most people feel stronger and clearer when fasting and can go about their usual routines with no trouble, though might go through short periods of weakness. Lots of water and liquid intake is always recommended in every fasting program I've read about. It sounds to me like you are mainly feeling week and dehydrated. It may not be a popular opinion, here or in the fasting forums, but I personally feel that fasts are pretty intense and should be done really carefully with the knowledge and experience behind it to know what to expect, or some help from someone who has that. I think most people who post in these forums are experimenting, and you have to take with a grain of salt everything you read (including what I would tell you) because what works well for one person might be completely wrong for another. I have a bad gut feeling that you are alone and attempting something pretty extreme, and I'm quite concerned for your safety. A 120 day urine fast sounds to me like a death sentence for anyone other than a Yogi or someone so spiritually trained that they can get through something like that.
Maybe a juice fast or a light raw diet, gentle potassium broths, stuff like that, might be better for your at this time. I am just getting a bad feeling that you're in trouble, and I'm kind of surprised nobody else here has said anything.
I also have spent a lot of time over in the Ask Barefoot forum, and he advocates an orange juice fast up to as long as 40 days, though most people don't go that long. There are nutrients, sugars, potassium in the oranges, apparently, that keep your body nourished while cleansing. Sometimes people will take a few raw almonds or a tablespoon of olive oil to keep the liver active during the fast. He also says to stop the fast if you stop eliminating, that you can become toxic very quickly if you are not getting even watery bowel movements.
Have you not found urine therapy with drinking it in the morning and staying on a normal clean diet to be beneficial? My 2 cents is that you need to be careful, and your intuition might be telling you that you are in over your head with this one.