I was just reading Isabel Moser's account(in "how and when to be your own doctor")of her 42 days on water, and she got to 85 pounds at 5'7. She admits wanting to hide from the alarmed looks of others--but you will not get that low, likely.
I fasted 29 days--don't know how much I lost, because I don't have a scale, but I know I looked a bit haggard at the end. Felt good though. Regardless of the lows, I knew without question what I was doing was ONLY good--in the bigger picture. I never suffered from constipation -- (barring a single day on rare occasions, of travelling or something. That sounds like the coffee put you into serious water deficit. Sipping hot boiled water can be pleasant, esp heading into your third week--when you might lose the taste for water.
I'd try to overlook the ego's voice, which is very much on about pleasing other people to get what it wants, (attention, reinforcement,)and 'fitting in', whereas You are so much more than the ego. It does not even KNOW about the radiant Self you really are, so it fears its demise, and will talk 'small' to you. Water Fasting takes stepping back from your thoughts and others' beliefs, not battling them, just stepping back into your greater self, to assume more of a witness perspective.
As one faster put it, it helps to "have imperishable patience". :-) With self and the world.
I feel/have felt my best at about 103 at 5'4. Would love to be 5'7 but it's not to be!(I did weigh myself back when I weighed this much, in 2000-2003. Now I'm probably 20 pounds over that ideal. I'm also almost 56, and there seems to be a period of adjusting to menopause. I firmly believe Water Fasting is The best thing a person can do, in their life--physically, and to break the enslavement of the mind that's been conditioned at every turn to serve the ego.
hang in there!
And do remember to break the fast on an Up.This might mean you don't go to 21 days. When you break on an up, the whole process of re-feeding and gaining back good, top quality flesh, goes so much easier and faster.