I’m two weeks in, already went through Keto flu, but suddenly I have such weakness in my legs and butt the last 2 days. I lost 6.5 lbs the first 10 days; maybe too much too fast? Maybe I’m not eating enough? I’m only about 15-20 po7nds over weight total.
Thanks everyone.
most likely an electrolyte issue. its common with a very low carb diet. search “ketoaid” and go from there.
I take a lot of Icelandic flake salt, magnesium and potassium. Most likely you have electrolytes deficiency specially if you are drinking all the water.
I had a very significant drop in energy in the first few weeks…a pregnant woman ran past me on a flight of stairs 
Give your body time to adjust, fluids, electrolytes…you’ll feel better soon 
That was all water while depleting your glycogen stores.
I’d also suggest electrolytes - I have borderline low blood pressure on keto, and I have to work to get enough water & salt. A dip of salt and a glass of water might be all you need to re-energize, or you might need to add an electrolyte drink on a regular basis like I have. Home-made “keto-aide” recipes abound in here; I’m lazy and also at time and space premiums when I’m driving (I drive a big rig with my hubby), so I use a commercial one called Ultima Replenisher (Amazon) and I also take salt tablets daily. Just experiment to find what keeps you feeling good. We call it your “N=1” - your own research project.
ONE MORE EDIT - if you exercise regularly, it might be wise to back off on it a bit until you are completely fat-adapted. Your body will thank you, and you can ease back in to your regular routine later.
I had a similar experience feeling this way. I have added a combo supplement of “ calcium-magnesium-zin” 3 tabs each day. It has helped.