I lost weight because i feel bad when i eat i feel like it knives.?

Weight Loss: Weight loss isn't always a good thing especially if caused by inability to eat which results in poor nutrition. Depending on the timing of food intake and pain, which I am guessing is stomach pains, will help determine cause. It is important to find the cause rather than cover up symptoms. Without proper nutrition, more negative health effects will start occuring down the line.

Gall bladder trouble: If you have pain relieved by meals, you could effectively be covering up ulcers. If you have pain caused by meals, you could be having gall stones. The gall bladder is necessary for the digestion of fats, so meals that are fatty/greasy/buttery really set off abdominal pain, usually under the right ribs. Consider getting an ultrasound to rule out an inflamed gall bladder that may need to be removed.