The weakness you may be facing could be due to a lot of causes, with only so much history it's very difficult to say any one exact.
Here are a few things you could consider.
Have a high protein diet.
Include foods that are very much rich in iron.
Have milk and other dairy products because they are rich in calcium.
Additionally you could take a multivitamin supplement daily after food.
If it still persists, Consult a physician near you.