The problem you mentioned is you are under weight.
You are 19 and height is 6ft and weight is only 45kg i.e your wt is very low.
It is utmost necessary that you increase your wt and your problem will go.
Take more protein,more fat and more carbohydrate
More milk with fat,cheese,paneer,eggs,
Have more cereals,pulses.
Go for B complex,multivitamin
and calcium supplements
Ok and bye.