I need to know something about my weightloss if anyone can help please help me.

What exactly do you need to know? It is difficult for people to gauge whether or not they can help you without knowing what you need.

Last week i tried sandwich ( omlette tomato slice cucumber slice and bread )
next day i felt very low in energy.

i felt dehydrated ..

can anyone tell why it happened

Not enough protein and not enough water. How much sodium was in the Omelet?

Was that all you ate? Post everything you ate so we can get a better picture of your food intake.

it was not only that I ate in whole day I ate that after all my meals of the day i tried it in evening. which can mean i ate 3400 calories of my regular meals then I ate that sandwich which gave me dehydration

it was not only that I ate in whole day I ate that after all my meals of the day i tried it in evening. which can mean i ate 3400 calories of my regular meals then I ate that sandwich which gave me dehydration