From some past days i am feeling weak and also lazy.how to cure it?

Weak & lazy: It's normal to feel "lazy" every now & then and not want to work or study. So unless you have a test, project or deadline due, take a break. Read a book. Watch a movie. Exercise! get outdoors for a hike. Hang out w/family & friends. Do something you enjoy. If "weakness" persists, go see your doctor. Could be anemia, hypothyroidism, depression, etc.

Need evaluation: There are a multitude of causes for feeling weak and lazy, e.g. From infection, grief, poor nutritional status (including eating disorder & excessive exercise), poor sleep/insomnia, medication side effects, other illnesses (depression, autimmune disease, cancer, severe pain, etc). This is something that, if it continues or interferes with your functioning, warrants evaluation by your doctor.