I had same symptoms when I (got) diabetes at 12.
Lost 15 lbs in a week. Drank tons of water and liquid,
but was very very thirsty - and nausea.
And very sleepy.
.
Dad took me to doctor - blood sugar was way up there.
So ended up in hospital for 4 days - getting regulated
on insulin.
.
Felt miles better in 2 weeks, but was hard at 12 getting
used to all this. Gained weight back to normal, and
energy too.
.
Your symptoms sound very very much like very high
blood sugar - which I occassionally get when my insulin
isn't working right - or I forgot to take my shot.
See a internal med doctor - or at least get a bloodsugar
meter and some strips and check your bloodsugar.
Good luck , bill11931